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XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
MAY 2007 REV. 1.1.3
GENERAL DESCRIPTION
The XR16L2551 (L2551) is a low voltage dual universal asynchronous receiver and transmitter (UART) with 5 Volt tolerant inputs. The device includes additional capability over the ST16C2550: Intel and Motorola data bus interface selection, hardware and software flow control, infrared encoder/ decoder, sleep mode and a PowerSave mode for battery operation. The L2551's enhanced register set is compatible to the ST16C2550 and XR16L2550. It supports the Exar's enhanced features of 16 bytes of TX and RX FIFOs and a complete modem interface. Onboard registers provide the user with operational status and data error tags. An internal loopback capability allows onboard diagnostics. Independent programmable baud rate generator is provided in each channel to support data rates up to 3.125 Mbps.
NOTE:
1 Covered by U.S. Patent #5,649,122.
FEATURES
* 2.25 to 5.5 Volt Operation * 5 Volt Tolerant Inputs * Intel or Motorola Bus Interface Select (16/68#)
pin
* Pin-to-pin compatible to XR16L2751CM * Two Independent UARTs
Up to 3.125 Mbps at 5V, 2 Mbps at 3.3V, and 1 Mbps at 2.5V with external clock input Up to 1.5 Mbps at 5V, 1.25 Mbps at 3.3V and 1 Mbps at 2.5V with crystal clock input 16 bytes of Transmit and Receive FIFOs Automatic RTS/CTS hardware flow control Automatic Xon/Xoff software flow control Wireless infrared encoder/decoder Receive FIFO trigger levels select Programmable character lengths (5, 6, 7 or 8) with even, odd, forced or no parity Full Modem Interface (CTS#, RTS#, DSR#, DTR#, RI#, CD#) in the 48-TQFP package

APPLICATIONS
* Battery Operated Instruments * Data Port Adapters * Handheld Appliances * Radio Frequency Data Modems * Base Stations * USB Hubs * Industrial Automation Controls
FIGURE 1. XR16L2551 BLOCK DIAGRAM
* Sleep Mode with PowerSave feature for battery
operation
* Industrial Temperature range * Tiny 32-QFN, no lead package (5x5x0.9mm) * 48-TQFP Package
PwrSave A2:A0 D7:D0 IOR# (VCC) IOW# (R/W#) CSA# (CS#) CSB# (A3) INTA (IRQ#) INTB (logic 0) TXRDYA# TXRDYB# RXRDYA# RXRDYB# Reset (Reset#) 16/68#
*5 Volt Tolerant Inputs
2.25 to 5.5 Volt VCC GND
UART Channel A UART Regs BRG 16 Byte TX FIFO TX & RX IR ENDEC TXA, RXA, RTSA#, CTSA#, ( DTR#, DSR# CD#, RIA#, OP2A# )
16 Byte RX FIFO TXB, RXB, RTSB#, CTSB#, ( DTRB#, DSRB# CDB#, RIB#, OP2B# ) XTAL1 XTAL2
Intel or Motorola Data Bus Interface
UART Channel B (same as Channel A)
Crystal Osc/Buffer
2551BLK
Exar Corporation 48720 Kato Road, Fremont CA, 94538 * (510) 668-7000 * FAX (510) 668-7017 * www.exar.com
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE FIGURE 2. PIN OUT ASSIGNMENT
REV. 1.1.3
CTSA#
VCC
30
29
26
32
31
28
27
25
30
29
26
32
31
28
D6 D7 RXB RXA TXA TXB CSA# CSB#
1 2 3 4 5 6 7 8 11 13 12 14 10 15 16 9
24 23 22
RESET RTSA# INTA INTB A0 A1 A2 16/68# A3 (CSB#) 8 11 13 12 14 RTSB# 15 10 16 9 17 16/68# GND VCC D6 D7 RXB RXA TXA TXB CS# 1 2 3 4 5 6 7 24 23 22 RESET# (Reset) RTSA# IRQ# NC (INTB) A0 A1 A2
XR16L2551 32-pin QFN in 16 (Intel) Mode
21 20 19 18 17
XR16L2551 32-pin QFN in 68 (Motorola) Mode
27
25
CTSA#
D4
D3
D2
D1
D5
D0
VCC
D4
D5
D3
D2
D1
D0
21 20 19 18
PWRSAVE
GND
RTSB#
CTSB#
XTAL2
IOW#
XTAL1
IOR#
PWRSAVE
XTAL2
TXRDYA#
TXRDYA#
DSRA#
VCC (IOR#)
CTSB#
XTAL1
R/W#
GND
CTSA#
DSRA#
VCC
VCC
NC
CTSA# 38
CDA#
RIA#
RIA#
CDA#
48
40
48
45
43
42
41
38
37
45
43
42
41
40
47
46
44
47
46
39
44
D5 D6 D7 RXB RXA TXRDYB# TXA TXB
1 2 3 4 5 6 7 8
36 RESET 35 34 33 32 DTRB# DTRA# RTSA# OP2A# RXRDYA# INTA INTB A0 A1 A2 NC
39
37
NC
D4
D3
D4
D2
D1
D0
D3
D2
D1
D0
D5 D6 D7 RXB RXA TXRDYB# TXA TXB OP2B#
1 2 3 4 5 6 7 8 9
36 35 34 33 32
RESET# DTRB# DTRA# RTSA# OP2A# RXRDYA# IRQ# NC A0 A1 A2 NC
XR16L2551 48-pin TQFP in 16 (Intel) Mode
31 30 29 28 27 26 25
XR16L2551 48-pin TQFP in 68 (Motorola) Mode)
31 30 29 28 27 26 25
OP2B# 9 CSA# 10 CSB# 11 PWRSAVE 12 15 19 13 18 20 22 23 16 21 14 17 24
CS# 10 A3 11
PWRSAVE 12 15 13 18 19 20 22 16 14 17 21 23 CTSB# 24 16/68#
GND
RTSB#
CTSB#
GND
RXRDYB#
RXRDYB#
DSRB#
VCC
DSRB#
RTSB#
RIB#
XTAL2
XTAL2
CDB#
16/68#
CDB#
IOW#
XTAL1
XTAL1
IOW#
IOR#
RIB#
VCC
GND
ORDERING INFORMATION
PART NUMBER XR16L2551IL XR16L2551IM PACKAGE 32-Lead QFN 48-Lead TQFP OPERATING TEMPERATURE RANGE -40C to +85C -40C to +85C DEVICE STATUS Active Active
2
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
PIN DESCRIPTIONS
Pin Description
NAME 32-QFN PIN # 48-TQFP PIN # TYPE DESCRIPTION
DATA BUS INTERFACE A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 IOR# (VCC) 18 19 20 2 1 32 31 30 29 28 27 14 26 27 28 3 2 1 48 47 46 45 44 19 I Address data lines [2:0]. These 3 address lines select one of the internal registers in UART channel A/B during a data bus transaction.
IO
Data bus lines [7:0] (bidirectional).
I
When 16/68# pin is at logic 1, the Intel bus interface is selected and this input becomes read strobe (active low). The falling edge instigates an internal read cycle and retrieves the data byte from an internal register pointed by the address lines [A2:A0], puts the data byte on the data bus to allow the host processor to read it on the rising edge. When 16/68# pin is at logic 0, the Motorola bus interface is selected and this input is not used and should be connected to VCC. When 16/68# pin is at logic 1, it selects Intel bus interface and this input becomes write strobe (active low). The falling edge instigates the internal write cycle and the rising edge transfers the data byte on the data bus to an internal register pointed by the address lines. When 16/68# pin is at logic 0, the Motorola bus interface is selected and this input becomes read (logic 1) and write (logic 0) signal. When 16/68# pin is at logic 1, this input is chip select A (active low) to enable channel A in the device. When 16/68# pin is at logic 0, this input becomes the chip select (active low) for the Motorola bus interface. When 16/68# pin is at logic 1, this input is chip select B (active low) to enable channel B in the device. When 16/68# pin is at logic 0, this input becomes address line A3 which is used for channel selection in the Motorola bus interface. Input logic 0 selects channel A and logic 1 selects channel B. When 16/68# pin is at logic 1 for Intel bus interface, this output becomes channel A interrupt output. The output state is defined by the user through the software setting of MCR[3]. INTA is set to the active mode and OP2A# output to a logic 0 when MCR[3] is set to a logic 1. INTA is set to the three state mode and OP2A# to a logic 1 when MCR[3] is set to a logic 0. See MCR[3]. When 16/68# pin is at logic 0 for Motorola bus interface, this output becomes device interrupt output (active low, open drain). An external pull-up resistor is required for proper operation.
IOW# (R/W#)
12
15
I
CSA# (CS#)
7
10
I
CSB# (A3)
8
11
I
INTA (IRQ#)
22
30
O
3
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE Pin Description
NAME INTB (NC) 32-QFN PIN # 21 48-TQFP PIN # 29 TYPE O DESCRIPTION When 16/68# pin is at logic 1 for Intel bus interface, this output becomes channel B interrupt output. The output state is defined by the user and through the software setting of MCR[3]. INTB is set to the active mode and OP2B# output to a logic 0 when MCR[3] is set to a logic 1. INTB is set to the three state mode and OP2B# to a logic 1 when MCR[3] is set to a logic 0. See MCR[3]. When 16/68# pin is at logic 0 for Motorola bus interface, this output is not used and will stay at logic zero level. Leave this output unconnected.
REV. 1.1.3
TXRDYA#
-
43
O
UART channel A Transmitter Ready (active low). The output provides the TX FIFO/THR status for transmit channel A. If it is not used, leave it unconnected.
UART channel A Receiver Ready (active low). This output provides the RX FIFO/RHR status for receive channel A. If it is not used, leave it unconnected. UART channel B Transmitter Ready (active low). The output provides the TX FIFO/THR status for transmit channel B. If it is not used, leave it unconnected. UART channel B Receiver Ready (active low). This output provides the RX FIFO/RHR status for receive channel B. If it is not used, leave it unconnected.
RXRDYA#
-
31
O
TXRDYB#
-
6
O
RXRDYB#
-
18
O
MODEM OR SERIAL I/O INTERFACE TXA RXA 5 4 7 5 O I UART channel A Transmit Data. If it is not used, leave it unconnected. UART channel A Receive Data. Normal receive data input must idle at logic 1 condition. If it is not used, tie it to VCC or pull it high via a 100k ohm resistor. UART channel A Request-to-Send (active low) or general purpose output. If it is not used, leave it unconnected. UART channel A Clear-to-Send (active low) or general purpose input. This input should be connected to VCC when not used. UART channel A Data-Terminal-Ready (active low) or general purpose output. If it is not used, leave it unconnected. UART channel A Data-Set-Ready (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. UART channel A Carrier-Detect (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. UART channel A Ring-Indicator (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART.
RTSA# CTSA# DTRA# DSRA#
23 25 -
33 38 34 39
O I O I
CDA#
-
40
I
RIA#
-
41
I
4
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
Pin Description
NAME OP2A# 32-QFN PIN # 48-TQFP PIN # 32 TYPE O DESCRIPTION Output Port 2 Channel A - The output state is defined by the user and through the software setting of MCR[3]. INTA is set to the active mode and OP2A# output to a logic 0 when MCR[3] is set to a logic 1. INTA is set to the three state mode and OP2A# to a logic 1 when MCR[3] is set to a logic 0. This output should not be used as a general output else it will disturb the INTA output functionality. If it is not used at all, leave it unconnected. UART channel B Transmit Data. If it is not used, leave it unconnected. UART channel B Receive Data. Normal receive data input must idle at logic 1 condition. If it is not used, tie it to VCC or pull it high via a 100k ohm resistor. UART channel B Request-to-Send (active low) or general purpose output. If it is not used, leave it unconnected. UART channel B Clear-to-Send (active low) or general purpose input. This input should be connected to VCC when not used. UART channel B Data-Terminal-Ready (active low) or general purpose output. If it is not used, leave it unconnected. UART channel B Data-Set-Ready (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. UART channel B Carrier-Detect (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. UART channel B Ring-Indicator (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. Output Port 2 Channel B - The output state is defined by the user and through the software setting of MCR[3]. INTB is set to the active mode and OP2B# output to a logic 0 when MCR[3] is set to a logic 1. INTB is set to the three state mode and OP2B# to a logic 1 when MCR[3] is set to a logic 0. This output should not be used as a general output else it will disturb the INTB output functionality. If it is not used, leave it unconnected.
TXB RXB
6 3
8 4
O I
RTSB# CTSB# DTRB# DSRB#
15 16 -
22 23 35 20
O I O I
CDB#
-
16
I
RIB#
-
21
I
OP2B#
-
9
O
ANCILLARY SIGNALS XTAL1 XTAL2 16/68# 10 11 17 13 14 24 I O I Crystal or external clock input. Crystal or buffered clock output. Intel or Motorola Bus Select. When 16/68# pin is at logic 1, 16 or Intel Mode, the device will operate in the Intel bus type of interface. When 16/68# pin is at logic 0, 68 or Motorola mode, the device will operate in the Motorola bus type of interface.
5
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE Pin Description
NAME PwrSave 32-QFN PIN # 9 48-TQFP PIN # 12 TYPE I DESCRIPTION PowerSave (active high). This feature isolates the L2551's data bus interface from the host preventing other bus activities that cause higher power drain during sleep mode. See Sleep Mode with Auto Wake-up and PowerSave Feature section for details. When 16/68# pin is at logic 1 for Intel bus interface, this input becomes RESET (active high). When 16/68# pin is at logic 0 for Motorola bus interface, this input becomes RESET# (active low). A 40 ns minimum active pulse on this pin will reset the internal registers and all outputs of channel A and B. The UART transmitter output will be held at logic 1, the receiver input will be ignored and outputs are reset during reset period (see UART Reset Conditions). 2.25V to 5.5V power supply. All inputs are 5V tolerant. Power supply common, ground. The center pad on the backside of the 32-QFN package is metallic and should be connected to GND on the PCB. The thermal pad size on the PCB should be the approximate size of this center pad and should be solder mask defined. The solder mask opening should be at least 0.0025" inwards from the edge of the PCB thermal pad. No Connection. These pins are not connected internally. But if there is a possibility of migrating to the XR16L2751 for future needs, please refer to the XR16L2751 datasheet to determine if these pins should be connected to VCC or GND.
REV. 1.1.3
RESET (RESET#)
24
36
I
VCC GND GND
26 13 Center Pad
42 17 N/A
Pwr Pwr Pwr
N.C.
-
25, 37
Pin type: I=Input, O=Output, IO= Input/output, OD=Output Open Drain.
6
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
1.0 PRODUCT DESCRIPTION The XR16L2551 (L2551) provides serial asynchronous receive data synchronization, parallel-to-serial and serial-to-parallel data conversions for both the transmitter and receiver sections. These functions are necessary for converting the serial data stream into parallel data that is required with digital data systems. Synchronization for the serial data stream is accomplished by adding start and stop bits to the transmit data to form a data character (character orientated protocol). Data integrity is ensured by attaching a parity bit to the data character. The parity bit is checked by the receiver for any transmission bit errors. The electronic circuitry to provide all these functions is fairly complex especially when manufactured on a single integrated silicon chip. The L2551 represents such an integration with greatly enhanced features. The L2551 is fabricated with an advanced CMOS process.
Transmit and Receive FIFOs (16 Bytes each) The L2551 is an upward solution that provides a dual UART capability with 16 bytes of transmit and receive FIFO memory, instead of none in the 16C2450. The L2551 is designed to work with high speed modems and shared network environments, that require fast data processing time. Increased performance is realized in the L2551 by the transmit and receive FIFO's. This allows the external processor to handle more networking tasks within a given time. For example, the ST16C2450 without a receive FIFO, will require unloading of the RHR in 93 microseconds (This example uses a character length of 11 bits, including start/stop bits at 115.2 Kbps). This means the external CPU will have to service the receive FIFO less than every 100 microseconds. However with the 16 byte FIFO in the L2551, the data buffer will not require unloading/loading for 1.53 ms. This increases the service interval giving the external CPU additional time for other applications and reducing the overall UART interrupt servicing time. In addition, the 4 selectable receive FIFO trigger interrupt levels is uniquely provided for maximum data throughput performance especially when operating in a multi-channel environment. The FIFO memory greatly reduces the bandwidth requirement of the external controlling CPU, increases performance, and reduces power consumption.
Data Bus Interface, Intel or Motorola Type The L2551 provides a single host interface for the 2 UARTs and supports Intel or Motorola microprocessor (CPU) data bus interface. The Intel bus compatible interface allows direct interconnect to Intel compatible type of CPUs using IOR#, IOW# and CSA# or CSB# inputs for data bus operation. The Motorola bus compatible interface instead uses the R/W#, CS# and A3 signals for data bus transactions. Few data bus interface signals change their functions depending on user's selection, see pin description for details. The Intel and Motorola bus interface selection is made through the 16/68# pin (pin 24 for 48-TQFP package and pin 17 for 32-QFN package).
Enhanced Features The XR16L2551 integrates the functions of 2 enhanced 16C550 Universal Asynchronous Receiver and Transmitter (UART). Its features set is compatible to the XR16L2550 device but offers Intel or Motorola data bus interface and PowerSave to isolate the data bus interface during Sleep mode. Each UART is independently controlled having its own set of device configuration registers. The configuration registers set is 16550 UART compatible for control, status and data transfer. Additionally, each UART channel has automatic RTS/CTS hardware flow control, automatic Xon/Xoff and special character software flow control, infrared encoder and decoder (IrDA ver 1.0), programmable baud rate generator with a prescaler of divide by 1 or 4, and data rate up to 3.125 Mbps at 5V with a 50 MHz external clock.
The rich feature set of the L2551 is available through internal registers. Selectable receive FIFO trigger levels, selectable TX and RX baud rates, and modem interface controls are all standard features. Following a power on reset or an external reset (and operating in 16 or Intel Mode), the L2551 is functionally and software compatible with the previous generation ST16C2450 and ST16C2550.
7
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE 2.0 FUNCTIONAL DESCRIPTIONS 2.1 CPU Interface
REV. 1.1.3
The CPU interface is 8 data bits wide with 3 address lines and control signals to execute data bus read and write transactions. The L2551 data interface supports the Intel compatible types of CPUs and it is compatible to the industry standard 16C550 UART. No clock (oscillator nor external clock) is required to operate a data bus transaction. Each bus cycle is asynchronous using CSA/B#, IOR# and IOW# or CS#, R/W# and A3 inputs. Both UART channels share the same data bus for host operations. A typical data bus interconnection for Intel and Motorola mode is shown in Figure 3. FIGURE 3. XR16L2751 TYPICAL INTEL/MOTOROLA DATA BUS INTERCONNECTIONS
D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 IOR# IOW# UART_CSA# UART_CSB# UART_INTA UART_INTB TXRDYA# RXRDYA# TXRDYB# RXRDYB# UART_RESET
D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 IOR# IOW# CSA# CSB# INTA INTB TXRDYA# RXRDYA# TXRDYB# RXRDYB# RESET
VCC TXA RXA DTRA# RTSA# CTSA# DSRA# CDA# RIA# OP2A#
2.25 to 5.5 Volt VCC
UART Channel A
RS-232 Serial Interface
(no connect)
TXB RXB UART Channel B DTRB# RTSB# CTSB# DSRB# CDB# RIB# OP2B# (no connect) RS-232 Serial Interface
GND
Intel Data Bus Interconnections
D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 A3 VCC R/W# UART_CS# VCC UART Channel B D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 CSB# IOR# IOW# TXB CSA# RXB DTRB# RTSB# CTSB# DSRB# CDB# RIB# OP2B# (no connect) RS-232 Serial Interface UART Channel A
VCC TXA RXA DTRA# RTSA# CTSA# DSRA# CDA# RIA# OP2A#
2.25 to 5.5 Volt VCC
RS-232 Serial Interface
(no connect)
UART_IRQ# (no connect) TXRDYA# RXRDYA# TXRDYB# RXRDYB# UART_RESET#
INTA INTB TXRDYA# RXRDYA# TXRDYB# RXRDYB# RESET#
GND
Motorola Data Bus Interconnections
2.2
5-Volt Tolerant Inputs
The L2551 can accept up to 5V inputs even when operating at 3.3V or 2.5V. But note that if the L2551 is operating at 2.5V, its VOH may not be high enough to meet the requirements of the VIH of a CPU or a serial transceiver that is operating at 5V.
8
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
2.3
Device Reset
The RESET or RESET# input resets the internal registers and the serial interface outputs in both channels to their default state (see Table 14). An active high pulse of at least 40 ns duration will be required to activate the reset function in the device. 2.4 Device Identification and Revision
The L2551 provides a Device Identification code and a Device Revision code to distinguish the part from other devices and revisions. To read the identification code from the part, it is required to set the baud rate generator registers DLL and DLM both to 0x00. Now reading the content of the DLM will provide 0x02 to indicate L2551 and reading the content of DLL will provide the revision of the part; for example, a reading of 0x01 means revision A. 2.5 Channel A and B Selection
The UART provides the user with the capability to bi-directionally transfer information between an external CPU and an external serial communication device. A logic 0 on chip select pins, CSA# or CSB#, allows the user to select UART channel A or B to configure, send transmit data and/or unload receive data to/from the UART. Selecting both UARTs can be useful during power up initialization to write to the same internal registers, but do not attempt to read from both uarts simultaneously. Individual channel select functions are shown in Table 1. TABLE 1: CHANNEL A AND B SELECT IN 16 MODE
CSA# 1 0 1 0 CSB# 1 1 0 0 FUNCTION UART de-selected Channel A selected Channel B selected Channel A and B selected
During Motorola Bus Mode (16/68# pin connected to GND), the package interface pins are configured for connection with Motorola, and other popular microprocessor bus types. In this mode the L2551 decodes an additional address, A3, to select one of the UART ports. The A3 address decode function is used only when in the Motorola Bus Mode. See Table 2. Channel A and B Internal Registers TABLE 2: CHANNEL A AND B SELECT IN 68 MODE
CS# 1 0 0 A3 N/A 0 1 FUNCTION UART de-selected Channel A selected Channel B selected
Each UART channel in the L2551 has a standard register set for controlling, monitoring and data loading and unloading. The configuration register set is compatible to those already available in the standard single 16C550. These registers function as data holding registers (THR/RHR), interrupt status and control registers (ISR/IER), a FIFO control register (FCR), receive line status and control registers (LSR/LCR), modem status and control registers (MSR/MCR), programmable data rate (clock) divisor registers (DLL/DLM), and a user accessible scratch pad register (SPR). 2.6 DMA Mode
The device does not support direct memory access. The DMA Mode (a legacy term) in this document doesn't mean "direct memory access" but refers to data block transfer operation. The DMA mode affects the state of the RXRDY# A/B and TXRDY# A/B output pins. The transmit and receive FIFO trigger levels provide additional flexibility to the user for block mode operation. The LSR bits 5-6 provide an indication when the transmitter is
9
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
REV. 1.1.3
empty or has an empty location(s) for more data. The user can optionally operate the transmit and receive FIFO in the DMA mode (FCR bit-3=1). When the transmit and receive FIFO are enabled and the DMA mode is disabled (FCR bit-3 = 0), the L2551 is placed in single-character mode for data transmit or receive operation. When DMA mode is enabled (FCR bit-3 = 1), the user takes advantage of block mode operation by loading or unloading the FIFO in a block sequence determined by the programmed trigger level. The following table show their behavior. Also see Figure 20 through Figure 25.
TABLE 3: TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE
PINS FCR BIT-0=0 (FIFO DISABLED) FCR BIT-0=1 (FIFO ENABLED) FCR Bit-3 = 0 (DMA Mode Disabled) RXRDY# A/B 0 = 1 byte. 1 = no data. 0 = THR empty. 1 = byte in THR. 0 = at least 1 byte in FIFO 1 = FIFO empty. 0 = FIFO empty. 1 = at least 1 byte in FIFO. FCR Bit-3 = 1 (DMA Mode Enabled) 1 to 0 transition when FIFO reaches the trigger level, or time-out occurs. 0 to 1 transition when FIFO empties. 0 = FIFO has at least 1 empty location. 1 = FIFO is full.
TXRDY# A/B
2.7
INTA and INTB Outputs
The INTA and INTB interrupt output changes according to the operating mode and enhanced features setup. Table 4 and Table 5 summarize the operating behavior for the transmitter and receiver. Also see Figure 20 through Figure 25.
TABLE 4: INTA AND INTB PINS OPERATION FOR TRANSMITTER
FCR BIT-0 = 0 (FIFO DISABLED) INTA/B Pin 0 = a byte in THR 1 = THR empty FCR BIT-0 = 1 (FIFO ENABLED) 0 = at least 1 byte in FIFO 1 = FIFO empty
TABLE 5: INTA AND INTB PIN OPERATION FOR RECEIVER
FCR BIT-0 = 0 (FIFO DISABLED) INTA/B Pin 0 = no data 1 = 1 byte FCR BIT-0 = 1 (FIFO ENABLED) 0 = FIFO below trigger level 1 = FIFO above trigger level
2.8
Crystal Oscillator or External Clock Input
The L2551 includes an on-chip oscillator (XTAL1 and XTAL2) to produce a clock for both UART sections in the device. The CPU data bus does not require this clock for bus operation. The crystal oscillator provides a system clock to the Baud Rate Generators (BRG) section found in each of the UART. XTAL1 is the input to the oscillator or external clock buffer input with XTAL2 pin being the output. Please note that the input XTAL1 is not 5V tolerant and so the maximum at the pin should be VCC. For programming details, see "Programmable Baud Rate Generator."
10
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS
XTAL1
XTAL2 R1 0-120 (Optional)
R2 500 K - 1 M Y1 C1 22-47 pF C2 22-47 pF
1.8432 MHz to 24 MHz
The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant, fundamental frequency with 10-22 pF capacitance load, ESR of 20-120 ohms and 100 ppm frequency tolerance) connected externally between the XTAL1 and XTAL2 pins (see Figure 4), with an external 500 k to 1 M resistor across it. Alternatively, an external clock can be connected to the XTAL1 pin to clock the internal baud rate generator for standard or custom rates. Typical oscillator connections are shown in Figure 4. For further reading on oscillator circuit please see application note DAN108 on EXAR's web site. 2.9 Programmable Baud Rate Generator
A single baud rate generator is provided for the transmitter and receiver, allowing independent TX/RX channel control. The programmable Baud Rate Generator is capable of operating with a crystal frequency of up to 24 MHz. However, with an external clock input on XTAL1 pin and a 2K ohms pull-up resistor on XTAL2 pin (as shown in Figure 5) it can extend its operation up to 50 MHz (3.125Mbps serial data rate) at room temperature and 5.0V. FIGURE 5. EXTERNAL CLOCK CONNECTION FOR EXTENDED DATA RATE
External Clock
vcc gnd
XTAL1
VCC R1 2K XTAL2
11
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
REV. 1.1.3
To obtain maximum data rate, it is necessary to use full rail swing on the clock input. See external clock operating frequency over power supply voltage chart in Figure 6. FIGURE 6. OPERATING FREQUENCY CHART. REQUIRES A 2K OHMS PULL-UP RESISTOR ON XTAL2 PIN TO INCREASE OPERATING SPEED
Operating frequency for XR16L2551 with external clock and a 2K ohms pull-up resistor on XTAL2 pin.
XTAL1 External Clock Frequency in MHz.
80 70 60 50 40 30 3.0 3.5 4.0
-40oC 25oC 85oC
4.5 5.0 5.5
Suppy Voltage
The L2551 divides the basic external clock by 16. The basic 16X clock provides table rates to support standard and custom applications using the same system design. The Baud Rate Generator divides the input 16X clock by any divisor from 1 to 216 -1. The rate table is configured via the DLL and DLM internal register functions. Customized Baud Rates can be achieved by selecting the proper divisor values for the MSB and LSB sections of baud rate generator. Table 6 shows the standard data rates available with a 14.7456 MHz crystal or external clock at 16X sampling rate. When using a non-standard frequency crystal or external clock, the divisor value can be calculated for DLL/DLM with the following equation.
divisor (decimal) = (XTAL1 clock frequency) / (serial data rate x 16)
12
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
TABLE 6: TYPICAL DATA RATES WITH A 14.7456 MHZ CRYSTAL OR EXTERNAL CLOCK
OUTPUT Data Rate MCR Bit-7=0 400 2400 4800 9600 19.2k 38.4k 76.8k 153.6k 230.4k 460.8k 921.6k DIVISOR FOR 16x Clock (Decimal) 2304 384 192 96 48 24 12 6 4 2 1 DIVISOR FOR 16x Clock (HEX) 900 180 C0 60 30 18 0C 06 04 02 01 DLM PROGRAM VALUE (HEX) 09 01 00 00 00 00 00 00 00 00 00 DLL PROGRAM VALUE (HEX) 00 80 C0 60 30 18 0C 06 04 02 01 DATA RATE ERROR (%) 0 0 0 0 0 0 0 0 0 0 0
2.10
Transmitter
The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 16 bytes of FIFO which includes a byte-wide Transmit Holding Register (THR). TSR shifts out every data bit with the 16X internal clock. A bit time is 16 clock periods. The transmitter sends the start-bit followed by the number of data bits, inserts the proper parity-bit if enabled, and adds the stop-bit(s). The status of the FIFO and TSR are reported in the Line Status Register (LSR bit-5 and bit-6). 2.10.1 Transmit Holding Register (THR) - Write Only
The transmit holding register is an 8-bit register providing a data interface to the host processor. The host writes transmit data byte to the THR to be converted into a serial data stream including start-bit, data bits, parity-bit and stop-bit(s). The least-significant-bit (Bit-0) becomes first data bit to go out. The THR is the input register to the transmit FIFO of 16 bytes when FIFO operation is enabled by FCR bit-0. Every time a write operation is made to the THR, the FIFO data pointer is automatically bumped to the next sequential data location. 2.10.2 Transmitter Operation in non-FIFO Mode
The host loads transmit data to THR one character at a time. The THR empty flag (LSR bit-5) is set when the data byte is transferred to TSR. THR flag can generate a transmit empty interrupt (ISR bit-1) when it is enabled by IER bit-1. The TSR flag (LSR bit-6) is set when TSR becomes completely empty.
13
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE 2.10.3 Transmitter Operation in FIFO Mode FIGURE 7. TRANSMITTER OPERATION IN NON-FIFO MODE
REV. 1.1.3
Data Byte
Transmit Holding Register (THR)
THR Interrupt (ISR bit-1) Enabled by IER bit-1
16X Clock
Transmit Shift Register (TSR)
M S B
L S B
TXNOFIFO1
The host may fill the transmit FIFO with up to 16 bytes of transmit data. The THR empty flag (LSR bit-5) is set whenever the FIFO is empty. The THR empty flag can generate a transmit empty interrupt (ISR bit-1) when the transmit empty interrupt is enabled by IER bit-1. The TSR flag (LSR bit-6) is set when the FIFO and the TSR become empty. FIGURE 8. TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE
Transmit Data Byte
Transm it FIFO
THR Interrupt (ISR bit-1) falls below the programmed Trigger Level and then when becomes empty. FIFO is Enabled by FCR bit-0=1
Auto CTS Flow Control (CTS# pin) Flow Control Characters (Xoff1/2 and Xon1/2 Reg. Auto Software Flow Control
16X Clock
Transm it Data Shift Register (TSR)
T XF IF O 1
2.11
Receiver
The receiver section contains an 8-bit Receive Shift Register (RSR) and 16 bytes of FIFO which includes a byte-wide Receive Holding Register (RHR). The RSR uses the 16X for timing. It verifies and validates every bit on the incoming character in the middle of each data bit. On the falling edge of a start or false start bit, an internal receiver counter starts counting at the 16X. After 8 clocks the start bit period should be at the center of the start bit. At this time the start bit is sampled and if it is still a logic 0 it is validated. Evaluating the start bit in this manner prevents the receiver from assembling a false character. The rest of the data bits and stop bits are sampled and validated in this same manner to prevent false framing. If there were any error(s), they are reported in the LSR register bits 2-4. Upon unloading the receive data byte from RHR, the receive FIFO pointer is bumped and the error tags are immediately updated to reflect the status of the data byte in RHR register. RHR can generate a receive data ready interrupt upon receiving a character or delay until it reaches the FIFO trigger level. Furthermore, data delivery to the host is guaranteed by a receive data ready time-out interrupt
14
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
when data is not received for 4 word lengths as defined by LCR[1:0] plus 12 bits time. This is equivalent to 3.74.6 character times. The RHR interrupt is enabled by IER bit-0. 2.11.1 Receive Holding Register (RHR) - Read-Only
The Receive Holding Register is an 8-bit register that holds a receive data byte from the Receive Shift Register. It provides the receive data interface to the host processor. The RHR register is part of the receive FIFO of 16 bytes by 11-bits wide, the 3 extra bits are for the 3 error tags to be reported in LSR register. When the FIFO is enabled by FCR bit-0, the RHR contains the first data character received by the FIFO. After the RHR is read, the next character byte is loaded into the RHR and the errors associated with the current data byte are immediately updated in the LSR bits 2-4. FIGURE 9. RECEIVER OPERATION IN NON-FIFO MODE
16X Clock Receive Data Shift Register (RSR) Data Bit Validation
Receive Data Characters
Receive Data Byte and Errors
Error Tags in LSR bits 4:2
Receive Data Holding Register (RHR)
RHR Interrupt (ISR bit-2)
RXFIFO1
FIGURE 10. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
16X Clock Receive Data Shift Register (RSR) Data Bit Validation
Receive Data Characters
16 bytes by 11-bit wide FIFO Error Tags (16-sets)
Example : - RX FIFO trigger level selected at 8 bytes Data falls to 4
Receive Data FIFO
RTS# re-asserts when data falls below the flow control trigger level to restart remote transmitter. Enable by EFR bit-6=1, MCR bit-2. RHR Interrupt (ISR bit-2) programmed for desired FIFO trigger level. FIFO is Enabled by FCR bit-0=1 RTS# de-asserts when data fills above the flow control trigger level to suspend remote transmitter. Enable by EFR bit-6=1, MCR bit-2.
FIFO Trigger=8
Data fills to 14 Error Tags in LSR bits 4:2
Receive Data Byte and Errors
Receive Data
RXFIFO1
15
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE 2.12 Auto RTS (Hardware) Flow Control
REV. 1.1.3
Automatic RTS hardware flow control is used to prevent data overrun to the local receiver FIFO. The RTS# output is used to request remote unit to suspend/resume data transmission. The auto RTS flow control features is enabled to fit specific application requirement (see Figure 11): - Enable auto RTS flow control using EFR bit-6. - The auto RTS function must be started by asserting RTS# output pin (MCR bit-1 to logic 1 after it is enabled). - Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the RTS# pin makes a transition from low to high: ISR bit-5 will be set to logic 1. 2.13 Auto CTS Flow Control Automatic CTS flow control is used to prevent data overrun to the remote receiver FIFO. The CTS# input is monitored to suspend/restart the local transmitter. The auto CTS flow control feature is selected to fit specific application requirement (see Figure 11): - Enable auto CTS flow control using EFR bit-7. - Enable CTS interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt when the CTS# pin is de-asserted (logic 1): ISR bit-5 will be set to 1, and UART will suspend transmission as soon as the stop bit of the character in process is shifted out. Transmission is resumed after the CTS# input is reasserted (logic 0), indicating more data may be sent.
16
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
FIGURE 11. AUTO RTS AND CTS FLOW CONTROL OPERATION
Local UART UARTA Receiver FIFO Trigger Reached Auto RTS Trigger Level Transmitter Auto CTS Monitor RXA TXB Remote UART UARTB Transmitter Auto CTS Monitor Receiver FIFO Trigger Reached Auto RTS Trigger Level
RTSA# TXA
CTSB# RXB
CTSA# Assert RTS# to Begin Transmission 1 ON 2 7 ON 3 8 OFF
RTSB#
RTSA# CTSB# TXB
OFF
10 11
ON ON
Data Starts 4 RXA FIFO INTA (RXA FIFO Interrupt) Receive RX FIFO Data Trigger Level 5
6
Suspend
Restart 9
RTS High Threshold
RTS Low Threshold
12
RX FIFO Trigger Level
RTSCTS1
The local UART (UARTA) starts data transfer by asserting RTSA# (1). RTSA# is normally connected to CTSB# (2) of remote UART (UARTB). CTSB# allows its transmitter to send data (3). TXB data arrives and fills UARTA receive FIFO (4). When RXA data fills up to its receive FIFO trigger level, UARTA activates its RXA data ready interrupt (5) and continues to receive and put data into its FIFO. If interrupt service latency is long and data is not being unloaded, UARTA monitors its receive data fill level to match the upper threshold of RTS delay and de-assert RTSA# (6). CTSB# follows (7) and request UARTB transmitter to suspend data transfer. UARTB stops or finishes sending the data bits in its transmit shift register (8). When receive FIFO data in UARTA is unloaded to match the lower threshold of RTS delay (9), UARTA re-asserts RTSA# (10), CTSB# recognizes the change (11) and restarts its transmitter and data flow again until next receive FIFO trigger (12). This same event applies to the reverse direction when UARTA sends data to UARTB with RTSB# and CTSA# controlling the data flow.
17
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE 2.14 Auto Xon/Xoff (Software) Flow Control
REV. 1.1.3
When software flow control is enabled (See Table 13), the L2551 compares one or two sequential receive data characters with the programmed Xon or Xoff-1,2 character value(s). If receive character(s) (RX) match the programmed values, the L2551 will halt transmission (TX) as soon as the current character has completed transmission. When a match occurs, the Xoff (if enabled via IER bit-5) flag will be set and the interrupt output pin will be activated. Following a suspension due to a match of the Xoff character, the L2551 will monitor the receive data stream for a match to the Xon-1,2 character. If a match is found, the L2551 will resume operation and clear the flags (ISR bit-4). Reset initially sets the contents of the Xon/Xoff 8-bit flow control registers to a logic 0. Following reset the user can write any Xon/Xoff value desired for software flow control. Different conditions can be set to detect Xon/ Xoff characters (See Table 13) and suspend/resume transmissions. When double 8-bit Xon/Xoff characters are selected, the L2551 compares two consecutive receive characters with two software flow control 8-bit values (Xon1, Xon2, Xoff1, Xoff2) and controls TX transmissions accordingly. Under the above described flow control mechanisms, flow control characters are not placed (stacked) in the user accessible RX data buffer or FIFO. In the event that the receive buffer is overfilling and flow control needs to be executed, the L2551 automatically sends an Xoff message (when enabled) via the serial TX output to the remote modem. The L2551 sends the Xoff-1,2 characters two-character-times (= time taken to send two characters at the programmed baud rate) after the receive FIFO crosses the programmed trigger level. To clear this condition, the L2551 will transmit the programmed Xon-1,2 characters as soon as receive FIFO is less than one trigger level below the programmed trigger level. See Table 7 below. TABLE 7: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL
RX TRIGGER LEVEL 1 4 8 14 INT PIN ACTIVATION 1 4 8 14 XOFF CHARACTER(S) SENT (CHARACTERS IN RX FIFO) 1* 4* 8* 14* XON CHARACTER(S) SENT (CHARACTERS IN RX FIFO) 0 1 4 8
* After the trigger level is reached, an xoff character is sent after a short span of time (= time required to send 2 characters); for example, after 2.083ms has elapsed for 9600 baud and 8-bit word length, no parity and 1 stop bit setting.
2.15
Special Character Detect
A special character detect feature is provided to detect an 8-bit character when bit-5 is set in the Enhanced Feature Register (EFR). When this character (Xoff2) is detected, it will be placed in the FIFO along with normal incoming RX data. The L2551 compares each incoming receive character with Xoff-2 data. If a match exists, the received data will be transferred to FIFO and ISR bit-4 will be set to indicate detection of special character. Although the Internal Register Table shows Xon, Xoff Registers with eight bits of character information, the actual number of bits is dependent on the programmed word length. Line Control Register (LCR) bits 0-1 defines the number of character bits, i.e., either 5 bits, 6 bits, 7 bits, or 8 bits. The word length selected by LCR bits 0-1 also determines the number of bits that will be used for the special character comparison. Bit-0 in the Xon, Xoff Registers corresponds with the LSB bit for the receive character.
18
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
2.16
Infrared Mode
The L2551 UART includes the infrared encoder and decoder compatible to the IrDA (Infrared Data Association) version 1.0. The IrDA 1.0 standard that stipulates the infrared encoder sends out a 3/16 of a bit wide HIGH-pulse for each "0" bit in the transmit data stream. This signal encoding reduces the on-time of the infrared LED, hence reduces the power consumption. See Figure 12 below. The infrared encoder and decoder are enabled by setting MCR register bit-6 to a `1'. When the infrared feature is enabled, the transmit data output, TX, idles at logic zero level. Likewise, the RX input assumes an idle level of logic zero from a reset and power up, see Figure 12. Typically, the wireless infrared decoder receives the input pulse from the infrared sensing diode on the RX pin. Each time it senses a light pulse, it returns a logic 1 to the data bit stream. FIGURE 12. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
Character Start Data Bits 1 0 1 0 0 1 1 0 Stop 1 1/2 Bit Time 3/16 Bit Time
IrEncoder-1
TX Data
0
Transmit IR Pulse (TX Pin) Bit Time
Receive IR Pulse (RX pin)
Bit Time 1/16 Clock Delay
RX Data
0 Start
1
0
1
0
0
11
0
1 Stop
IRdecoder-
Data Bits Character
19
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE 2.17 Sleep Mode with Auto Wake-Up and PowerSave Feature
REV. 1.1.3
The L2551 supports low voltage system designs, hence, a sleep mode with auto wake-up and PowerSave feature is included to reduce power consumption when the device is not actively used. 2.17.1 Sleep Mode
All of these conditions must be satisfied for the L2551 to enter sleep mode:

no interrupts pending for both channels of the L2551 (ISR bit-0 = 1) divisor is a non-zero value (ie. DLL = 0x1) sleep mode of both channels are enabled (IER bit-4 = 1) modem inputs are not toggling (MSR bits 0-3 = 0) RX input pins are idling at a logic 1
The L2551 stops its crystal oscillator to conserve power in the sleep mode. User can check the XTAL2 pin for no clock output as an indication that the device has entered the sleep mode. The L2551 resumes normal operation by any of the following when PowerSave mode is disabled:

a receive data start bit transition (logic 1 to 0) a data byte is loaded to the transmitter, THR or FIFO a change of logic state on any of the modem or general purpose serial inputs: CTS#, DSR#, CD#, RI#
If the L2551 is awakened by any one of the above conditions, it will return to the sleep mode automatically after all interrupting conditions have been serviced and cleared. If the L2551 is awakened by the modem inputs, a read to the MSR is required to reset the modem inputs. In any case, the sleep mode will not be entered while an interrupt is pending from channel A or B. The L2551 will stay in the sleep mode of operation until it is disabled by setting IER bit-4 to a logic 0. A word of caution: owing to the starting up delay of the crystal oscillator after waking up from sleep mode, the first few receive characters may be lost. The number of characters lost during the restart also depends on your operating data rate. More characters are lost when operating at higher data rate. Also, it is important to keep RX A/B inputs idling at logic 1 or "marking" condition during sleep mode to avoid receiving a "break" condition upon the restart. This may occur when the external interface transceivers (RS-232, RS-485 or another type) are also put to sleep mode and cannot maintain the "marking" condition. To avoid this, the designer can use a 47k-100k ohm pull-up resistor on the RXA and RXB pins. 2.17.2 PowerSave Feature
If the address lines, data bus lines, IOW#, IOR#, CSA#, CSB#, and modem input lines remain steady when the L2551 is in sleep mode, the maximum current will be in the microamp range as specified in the DC Electrical Characteristics on page 36. If the input lines are floating or are toggling while the L2551 is in sleep mode, the current can be up to 100 times more. If not using the PowerSave feature, then an external buffer would be required to keep the address and data bus lines from toggling or floating to achieve the low current. But if the PowerSave feature is enabled (pin 12 of the 48-TQFP or pin 9 of the 32-QFN is connected to VCC), this will eliminate the need for an external buffer by internally isolating the address, data and control signals (see Figure 1 on page 1) from other bus activities that could cause wasteful power drain. The L2551 enters PowerSave mode when the PWRSAVE pin is connected to VCC and the L2551 is in sleep mode (see Sleep Mode section above). Since PowerSave mode isolates the address, data and control signals, the device will wake-up by:

a receive data start bit transition (logic 1 to 0) a change of logic state on any of the modem or general purpose serial inputs: CTS#, DSR#, CD#, RI#
The L2551 will return to the PowerSave mode automatically after a read to the MSR (to reset the modem inputs) and all interrupting conditions have been serviced and cleared. The L2551 will stay in the PowerSave mode of operation until it is disabled by setting IER bit-4 to a logic 0 and/or the PowerSave pin is connected to GND.
20
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE Internal Loopback
2.18
The L2551 UART provides an internal loopback capability for system diagnostic purposes. The internal loopback mode is enabled by setting MCR register bit-4 to logic 1. All regular UART functions operate normally. Figure 13 shows how the modem port signals are re-configured. Transmit data from the transmit shift register output is internally routed to the receive shift register input allowing the system to receive the same data that it was sending. The TX pin is held at logic 1 or mark condition while RTS# and DTR# are de-asserted, and CTS#, DSR# CD# and RI# inputs are ignored. Caution: the RX input pins must be held to a logic 1 during loopback test else upon exiting the loopback test the UART may detect and report a false "break" signal. Also, Auto RTS/CTS is not supported during internal loopback. FIGURE 13. INTERNAL LOOP BACK IN CHANNEL A AND B
VCC Transmit Shift Register (THR/FIFO) MCR bit-4=1 Internal Data Bus Lines and Control Signals Receive Shift Register (RHR/FIFO) VCC RTS# Modem / General Purpose Control Logic RTSA#/RTSB# TXA/TXB
RXA/RXB
CTS# VCC DTR#
CTSA#/CTSB# DTRA#/DTRB#
DSR# OP1# RI# VCC OP2#
DSRA#/DSRB# RIA#/RIB# OP2A#/OP2B#
CD#
CDA#/CDB#
21
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE 3.0 UART INTERNAL REGISTERS Each of the UART channel in the L2551 has its own set of configuration registers selected by address lines A0, A1 and A2 with CSA# or CSB# selecting the channel. The registers are 16C550 compatible. The complete register set is shown on Table 8 and Table 9....INTERNAL Register descriptions TABLE 8: UART CHANNEL A AND B UART INTERNAL REGISTERS
A2,A1,A0 ADDRESSES REGISTER READ/WRITE COMMENTS
REV. 1.1.3
16C550 COMPATIBLE REGISTERS 0 00 RHR - Receive Holding Register THR - Transmit Holding Register DLL - Div Latch Low Byte DLM - Div Latch High Byte DREV - Device Revision DVID - Device ID IER - Interrupt Enable Register ISR - Interrupt Status Register FCR - FIFO Control Register LCR - Line Control Register MCR - Modem Control Register LSR - Line Status Register Reserved MSR - Modem Status Register Reserved SPR - Scratch Pad Register ENHANCED REGISTERS 0 1 1 1 1 10 00 01 10 11 EFR - Enhanced Function Register Xon-1 - Xon Character 1 Xon-2 - Xon Character 2 Xoff-1 - Xoff Character 1 Xoff-2 - Xoff Character 2 Read/Write Read/Write Read/Write Read/Write Read/Write LCR = 0xBF Read-only Write-only Read/Write Read/Write Read/Write Read/Write Read/Write Read-only Write-only Read/Write Read/Write Read-only Write-only Read-only Write-only Read/Write LCR[7] = 1, LCR 0xBF, DLL = 0x00, DLM = 0x00 LCR[7] = 0 LCR 0xBF LCR[7] = 0
0 0 0 0 0 0
00 01 00 01 01 10
LCR[7] = 1, LCR 0xBF
0 1 1
11 00 01
LCR 0xBF
1
10
1
11
22
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
TABLE 9: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDRESS A2-A0 REG NAME READ/ WRITE BIT-7 BIT-6 BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0 COMMENT
16C550 Compatible Registers 000 000 001 RHR THR IER RD WR RD/WR Bit-7 Bit-7 0/ Bit-6 Bit-6 0/ Bit-5 Bit-5 0/ Xoff Int. Enable 0/ INT Source Bit-5 0 Bit-4 Bit-4 0/ Sleep Mode Enable 0/ INT Source Bit-4 0 Bit-3 Bit-3 Bit-2 Bit-2 Bit-1 Bit-1 Bit-0 Bit-0 LCR[7] = 0
CTS Int. RTS Int. Enable Enable 010 ISR RD FIFOs FIFOs Enabled Enabled
Modem RX Line TX RX Stat. Stat. Empty Data Int. Int. Int Int. Enable Enable Enable Enable INT INT INT INT Source Source Source Source Bit-3 Bit-2 Bit-1 Bit-0
LCR 0xBF DMA Mode Enable Parity Enable TX FIFO Reset Stop Bits RX FIFO Reset FIFOs Enable
010
FCR
WR
RX FIFO RX FIFO Trigger Trigger Divisor Enable Set TX Break
011
LCR
RD/WR
Set Parity
Even Parity
Word Word Length Length Bit-1 Bit-0
100
MCR
RD/WR
0/ BRG Prescaler
0/
0/
IR Mode XonAny ENable THR & TSR Empty RI# Input Bit-6 THR Empty
Internal Loopback Enable RX Break
OP2#/ Rsvd RTS# DTR# INT Output Output (OP1#) Output Control Control Enable RX Framing Error Delta CD# Bit-3 RX Parity Error Delta RI# Bit-2 RX Overrun Error Delta DSR# Bit-1 RX Data Ready Delta CTS# Bit-0
101
LSR
RD
RX FIFO Global Error CD# Input Bit-7
LCR 0xBF
110 111
MSR SPR
RD RD/WR
DSR# Input Bit-5
CTS# Input Bit-4
Baud Rate Generator Divisor 000 001 000 001 DLL DLM DREV DVID RD/WR RD/WR RD RD Bit-7 Bit-7 Bit-7 0 Bit-6 Bit-6 Bit-6 0 Bit-5 Bit-5 Bit-5 0 Bit-4 Bit-4 Bit-4 0 Bit-3 Bit-3 Bit-3 0 Bit-2 Bit-2 Bit-2 0 Bit-1 Bit-1 Bit-1 1 Bit-0 Bit-0 Bit-0 0 LCR[7] = 1 LCR 0xBF LCR[7]=1 DLL=0x00 DLM=0x00
23
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
REV. 1.1.3
TABLE 9: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDRESS A2-A0 REG NAME READ/ WRITE BIT-7 BIT-6 BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0 COMMENT
Enhanced Registers 010 EFR RD/WR Auto CTS Enable Auto RTS Enable Special Char Select
Enable IER [7:4], ISR [5:4], FCR[5:4], MCR[7:5]
Software Flow Cntl Bit-3 Bit-3 Bit-3 Bit-3 Bit-3
Software Flow Cntl Bit-2 Bit-2 Bit-2 Bit-2 Bit-2
Software Flow Cntl Bit-1 Bit-1 Bit-1 Bit-1 Bit-1
Software Flow Cntl Bit-0 Bit-0 Bit-0 Bit-0 Bit-0 LCR=0XBF
100 101 110 111
XON1 RD/WR XON2 RD/WR XOFF1 RD/WR XOFF2 RD/WR
Bit-7 Bit-7 Bit-7 Bit-7
Bit-6 Bit-6 Bit-6 Bit-6
Bit-5 Bit-5 Bit-5 Bit-5
Bit-4 Bit-4 Bit-4 Bit-4
4.0 INTERNAL REGISTER DESCRIPTIONS 4.1 Receive Holding Register (RHR) - Read- Only
SEE "RECEIVER" ON PAGE 14. 4.2 Transmit Holding Register (THR) - Write-Only
SEE "TRANSMITTER" ON PAGE 13. 4.3 Interrupt Enable Register (IER) - Read/Write
The Interrupt Enable Register (IER) masks the interrupts from receive data ready, transmit empty, line status and modem status registers. These interrupts are reported in the Interrupt Status Register (ISR). 4.3.1 IER versus Receive FIFO Interrupt Mode Operation
When the receive FIFO (FCR BIT-0 = 1) and receive interrupts (IER BIT-0 = 1) are enabled, the RHR interrupts (see ISR bits 2 and 3) status will reflect the following: A. The receive data available interrupts are issued to the host when the FIFO has reached the programmed trigger level. It will be cleared when the FIFO drops below the programmed trigger level. B. FIFO level will be reflected in the ISR register when the FIFO trigger level is reached. Both the ISR register status bit and the interrupt will be cleared when the FIFO drops below the trigger level. C. The receive data ready bit (LSR BIT-0) is set as soon as a character is transferred from the shift register to the receive FIFO. It is reset when the FIFO is empty. 4.3.2 IER versus Receive/Transmit FIFO Polled Mode Operation
When FCR BIT-0 equals a logic 1 for FIFO enable; resetting IER bits 0-3 enables the XR16L2551 in the FIFO polled mode of operation. Since the receiver and transmitter have separate bits in the LSR either or both can be used in the polled mode by selecting respective transmit or receive control bit(s). A. LSR BIT-0 indicates there is data in RHR or RX FIFO. B. LSR BIT-1 indicates an overrun error has occurred and that data in the FIFO may not be valid. C. LSR BIT 2-4 provides the type of receive data errors encountered for the data byte in RHR, if any. D. LSR BIT-5 indicates Transmit FIFO is empty. E. LSR BIT-6 indicates when both the transmit FIFO and TSR are empty. F. LSR BIT-7 indicates a data error in at least one character in the RX FIFO.
24
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
IER[0]: RHR Interrupt Enable The receive data ready interrupt will be issued when RHR has a data character in the non-FIFO mode or when the receive FIFO has reached the programmed trigger level in the FIFO mode.
* Logic 0 = Disable the receive data ready interrupt (default). * Logic 1 = Enable the receiver data ready interrupt.
IER[1]: THR Interrupt Enable This bit enables the Transmit Ready interrupt which is issued whenever the Transmit FIFO becomes empty. If the Transmit FIFO is empty when this bit is enabled, an interrupt will be generated.
* Logic 0 = Disable Transmit Ready interrupt (default). * Logic 1 = Enable Transmit Ready interrupt.
IER[2]: Receive Line Status Interrupt Enable If any of the LSR register bits 1, 2, 3 or 4 is a logic 1, it will generate an interrupt to inform the host controller about the error status of the current data byte in FIFO. LSR bit-1 generates an interrupt immediately when the character has been received. LSR bits 2-4 generate an interrupt when the character with errors is read out of the FIFO.
* Logic 0 = Disable the receiver line status interrupt (default). * Logic 1 = Enable the receiver line status interrupt.
IER[3]: Modem Status Interrupt Enable
* Logic 0 = Disable the modem status register interrupt (default). * Logic 1 = Enable the modem status register interrupt.
IER[4]: Sleep Mode Enable (requires EFR bit-4 = 1)
* Logic 0 = Disable Sleep Mode (default). * Logic 1 = Enable Sleep Mode. See Sleep Mode section for further details.
IER[5]: Xoff Interrupt Enable (requires EFR bit-4=1)
* Logic 0 = Disable the software flow control, receive Xoff interrupt. (default) * Logic 1 = Enable the software flow control, receive Xoff interrupt. See Software Flow Control section for
details. IER[6]: RTS# Output Interrupt Enable (requires EFR bit-4=1)
* Logic 0 = Disable the RTS# interrupt (default). * Logic 1 = Enable the RTS# interrupt. The UART issues an interrupt when the RTS# pin makes a transition
from low to high. IER[7]: CTS# Input Interrupt Enable (requires EFR bit-4=1)
* Logic 0 = Disable the CTS# interrupt (default). * Logic 1 = Enable the CTS# interrupt. The UART issues an interrupt when CTS# pin makes a transition from
low to high.
25
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE 4.4 Interrupt Status Register (ISR) - Read-Only
REV. 1.1.3
The UART provides multiple levels of prioritized interrupts to minimize external software interaction. The Interrupt Status Register (ISR) provides the user with six interrupt status bits. Performing a read cycle on the ISR will give the user the current highest pending interrupt level to be serviced, others are queued up to be serviced next. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt Source Table, Table 10, shows the data values (bit 0-5) for the interrupt priority levels and the interrupt sources associated with each of these interrupt levels. 4.4.1 Interrupt Generation:
* LSR is by any of the LSR bits 1, 2, 3 and 4. * RXRDY is by RX trigger level. * RXRDY Time-out is by a 4-char plus 12 bits delay timer. * TXRDY is by TX FIFO empty. * MSR is by any of the MSR bits 0, 1, 2 and 3. * Receive Xoff/Special character is by detection of a Xoff or Special character. * CTS# is when its transmitter toggles the input pin (from low to high) during auto CTS flow control. * RTS# is when its receiver toggles the output pin (from low to high) during auto RTS flow control.
4.4.2 Interrupt Clearing:
* LSR interrupt is cleared by a read to the LSR register (but flags and tags not cleared until character(s) that
generated the interrupt(s) has been emptied or cleared from FIFO).
* RXRDY interrupt is cleared by reading data until FIFO falls below the trigger level. * RXRDY Time-out interrupt is cleared by reading RHR. * TXRDY interrupt is cleared by a read to the ISR register or writing to THR. * MSR interrupt is cleared by a read to the MSR register. * Xoff interrupt is cleared by a read to ISR or when Xon character(s) is received. * Special character interrupt is cleared by a read to ISR or after the next character is received. * RTS# and CTS# flow control interrupts are cleared by a read to the MSR register.
]
TABLE 10: INTERRUPT SOURCE AND PRIORITY LEVEL
PRIORITY LEVEL 1 2 3 4 5 6 7 BIT-5 0 0 0 0 0 0 1 0 ISR REGISTER STATUS BITS BIT-4 0 0 0 0 0 1 0 0 BIT-3 0 1 0 0 0 0 0 0 BIT-2 1 1 1 0 0 0 0 0 BIT-1 1 0 0 1 0 0 0 0 BIT-0 0 0 0 0 0 0 0 1 LSR (Receiver Line Status Register) RXRDY (Receive Data Time-out) RXRDY (Received Data Ready) TXRDY (Transmit Ready) MSR (Modem Status Register) RXRDY (Received Xoff or Special character) CTS#, RTS# change of state None (default) SOURCE OF INTERRUPT
26
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
ISR[0]: Interrupt Status
* Logic 0 = An interrupt is pending and the ISR contents may be used as a pointer to the appropriate interrupt
service routine.
* Logic 1 = No interrupt pending (default condition).
ISR[3:1]: Interrupt Status These bits indicate the source for a pending interrupt at interrupt priority levels (See Interrupt Source Table 10). ISR[4]: Xoff or Special Character Interrupt Status This bit is enabled when EFR bit-4 is set to a logic 1. ISR bit-4 indicates that the receiver detected a data match of the Xoff character(s). If this is an Xoff interrupt, it can be cleared by a read to the ISR or when an Xon character is received. If it is a special character interrupt, it will automatically clear after the next character is received. ISR[5]: RTS#/CTS# Interrupt Status This bit is enabled when EFR bit-4 is set to a logic 1. ISR bit-5 indicates that the CTS# or RTS# has changed state from low to high. ISR[7:6]: FIFO Enable Status These bits are set to a logic 0 when the FIFOs are disabled. They are set to a logic 1 when the FIFOs are enabled. 4.5 FIFO Control Register (FCR) - Write-Only
This register is used to enable the FIFOs, clear the FIFOs, set the transmit/receive FIFO trigger levels, and select the DMA mode. The DMA, and FIFO modes are defined as follows: FCR[0]: TX and RX FIFO Enable
* Logic 0 = Disable the transmit and receive FIFO (default). * Logic 1 = Enable the transmit and receive FIFOs. This bit must be set to logic 1 when other FCR bits are
written or they will not be programmed. FCR[1]: RX FIFO Reset This bit is only active when FCR bit-0 is a `1'.
* Logic 0 = No receive FIFO reset (default) * Logic 1 = Reset the receive FIFO pointers and FIFO level counter logic (the receive shift register is not
cleared or altered). This bit will return to a logic 0 after resetting the FIFO. FCR[2]: TX FIFO Reset This bit is only active when FCR bit-0 is a `1'.
* Logic 0 = No transmit FIFO reset (default). * Logic 1 = Reset the transmit FIFO pointers and FIFO level counter logic (the transmit shift register is not
cleared or altered). This bit will return to a logic 0 after resetting the FIFO. FCR[3]: DMA Mode Select Controls the behavior of theTXRDY# and RXRDY# pins. See DMA operation section for details.
* Logic 0 = Normal Operation (default). * Logic 1 = DMA Mode.
FCR[5:4]: Reserved
27
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE FCR[7:6]: Receive FIFO Trigger Select (logic 0 = default, RX trigger level =1) These 2 bits are used to set the trigger level for the receive FIFO. The UART will issue a receive interrupt when the number of the characters in the FIFO crosses the trigger level. Table 11 shows the complete selections.
REV. 1.1.3
TABLE 11: RECEIVE FIFO TRIGGER LEVEL SELECTION
FCR BIT-7 0 0 1 1 FCR BIT-6 0 1 0 1 RECEIVE TRIGGER LEVEL 1 (default) 4 8 14 COMPATIBILITY 16C550, 16C2550, 16C2552, 16C554, 16C580 compatible.
4.6
Line Control Register (LCR) - Read/Write
The Line Control Register is used to specify the asynchronous data communication format. The word or character length, the number of stop bits, and the parity are selected by writing the appropriate bits in this register. LCR[1:0]: TX and RX Word Length Select These two bits specify the word length to be transmitted or received.
BIT-1 0 0 1 1
BIT-0 0 1 0 1
WORD LENGTH 5 (default) 6 7 8
LCR[2]: TX and RX Stop-bit Length Select The length of stop bit is specified by this bit in conjunction with the programmed word length.
BIT-2 0 1 1
WORD LENGTH 5,6,7,8 5 6,7,8
STOP BIT LENGTH (BIT TIME(S)) 1 (default) 1-1/2 2
LCR[3]: TX and RX Parity Select Parity or no parity can be selected via this bit. The parity bit is a simple way used in communications for data integrity check. See Table 12 for parity selection summary below.
* Logic 0 = No parity. * Logic 1 = A parity bit is generated during the transmission while the receiver checks for parity error of the
data character received.
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XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
LCR[4]: TX and RX Parity Select If the parity bit is enabled with LCR bit-3 set to a logic 1, LCR BIT-4 selects the even or odd parity format.
* Logic 0 = ODD Parity is generated by forcing an odd number of logic 1's in the transmitted character. The
receiver must be programmed to check the same format (default).
* Logic 1 = EVEN Parity is generated by forcing an even number of logic 1's in the transmitted character. The
receiver must be programmed to check the same format. LCR[5]: TX and RX Parity Select If the parity bit is enabled, LCR BIT-5 selects the forced parity format.
* LCR[5] = logic 0, parity is not forced (default). * LCR[5] = logic 1 and LCR[4] = logic 0, parity bit is forced to a logical 1 for the transmit and receive data. * LCR[5] = logic 1 and LCR[4] = logic 1, parity bit is forced to a logical 0 for the transmit and receive data.
TABLE 12: PARITY SELECTION
LCR BIT-5 LCR BIT-4 LCR BIT-3 X 0 0 1 1 X 0 1 0 1 0 1 1 1 1 PARITY SELECTION No parity Odd parity Even parity Force parity to mark, "1" Forced parity to space, "0"
LCR[6]: Transmit Break Enable When enabled, the Break control bit causes a break condition to be transmitted (the TX output is forced to a "space', logic 0, state). This condition remains, until disabled by setting LCR bit-6 to a logic 0.
* Logic 0 = No TX break condition (default). * Logic 1 = Forces the transmitter output (TX) to a "space", logic 0, for alerting the remote receiver of a line
break condition. LCR[7]: Baud Rate Divisors (DLL/DLM) Enable
* Logic 0 = Data registers are selected (default). * Logic 1 = Divisor latch registers are selected.
4.7 Modem Control Register (MCR) or General Purpose Outputs Control - Read/Write The MCR register is used for controlling the serial/modem interface signals or general purpose inputs/outputs. MCR[0]: DTR# Output The DTR# pin is a modem control output. If the modem interface is not used, this output may be used as a general purpose output.
* Logic 0 = Force DTR# output to a logic 1 (default). * Logic 1 = Force DTR# output to a logic 0.
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XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE MCR[1]: RTS# Output The RTS# pin is a modem control output. If the modem interface is not used, this output may be used as a general purpose output.
REV. 1.1.3
* Logic 0 = Force RTS# output to a logic 1 (default). * Logic 1 = Force RTS# output to a logic 0.
MCR[2]: Reserved OP1# is not available as an output pin on the L2551. But it is available for use during Internal Loopback Mode. In the Loopback Mode, this bit is used to write the state of the modem RI# interface signal. MCR[3]: OP2# Output / INT Output Enable This bit enables and disables the operation of INT, interrupt output. If INT output is not used, OP2# can be used as a general purpose output. This bit does not affect the IRQ# output during Motorola mode.
* Logic 0 = INT (A-B) outputs disabled (three state mode) and OP2# output set to a logic 1 (default). * Logic 1 = INT (A-B) outputs enabled (active mode) and OP2# output set to a logic 0.
MCR[4]: Internal Loopback Enable
* Logic 0 = Disable loopback mode (default). * Logic 1 = Enable local loopback mode, see loopback section and Figure 13.
MCR[5]: Xon-Any Enable
* Logic 0 = Disable Xon-Any function (for 16C550 compatibility, default). * Logic 1 = Enable Xon-Any function. In this mode, any RX character received will resume transmit operation.
The RX character will be loaded into the RX FIFO , unless the RX character is an Xon or Xoff character and the L2551 is programmed to use the Xon/Xoff flow control. MCR[6]: Infrared Encoder/Decoder Enable
* Logic 0 = Enable the standard modem receive and transmit input/output interface. (Default) * Logic 1 = Enable infrared IrDA receive and transmit inputs/outputs. The TX/RX output/input are routed to the
infrared encoder/decoder. The data input and output levels conform to the IrDA infrared interface requirement. While in this mode, the infrared TX output will be a logic 0 during idle data conditions. MCR[7]: Clock Prescaler Select
* Logic 0 = Divide by one. The input clock from the crystal or external clock is fed directly to the Programmable
Baud Rate Generator without further modification, i.e., divide by one (default).
* Logic 1 = Divide by four. The prescaler divides the input clock from the crystal or external clock by four and
feeds it to the Programmable Baud Rate Generator, hence, data rates become one forth. 4.8 Line Status Register (LSR) - Read Only
This register provides the status of data transfers between the UART and the host. LSR[0]: Receive Data Ready Indicator
* Logic 0 = No data in receive holding register or FIFO (default). * Logic 1 = Data has been received and is saved in the receive holding register or FIFO.
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XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
LSR[1]: Receiver Overrun Flag
* Logic 0 = No overrun error (default). * Logic 1 = Overrun error. A data overrun error condition occurred in the receive shift register. This happens
when additional data arrives while the FIFO is full. In this case the previous data in the receive shift register is overwritten. Note that under this condition the data byte in the receive shift register is not transferred into the FIFO, therefore the data in the FIFO is not corrupted by the error. An interrupt will be generated immediately if LSR interrupt is enabled (IER bit-2). LSR[2]: Receive Data Parity Error Flag
* Logic 0 = No parity error (default). * Logic 1 = Parity error. The receive character in RHR does not have correct parity information and is suspect.
This error is associated with the character available for reading in RHR. If the LSR interrupt is enabled (IER bit-2), an interrupt will be generated when the character is in the RHR. LSR[3]: Receive Data Framing Error Flag
* Logic 0 = No framing error (default). * Logic 1 = Framing error. The receive character did not have a valid stop bit(s). This error is associated with
the character available for reading in RHR. If the LSR interrupt is enabled (IER bit-2), an interrupt will be generated when the character is in the RHR. LSR[4]: Receive Break Flag
* Logic 0 = No break condition (default). * Logic 1 = The receiver received a break signal (RX was a logic 0 for at least one character frame time). In the
FIFO mode, only one break character is loaded into the FIFO. The break indication remains until the RX input returns to the idle condition, "mark" or logic 1. If the LSR interrupt is enabled (IER bit-2), an interrupt will be generated when the character is in the RHR. LSR[5]: Transmit Holding Register Empty Flag This bit is the Transmit Holding Register Empty indicator. This bit indicates that the transmitter is ready to accept a new character for transmission. In addition, this bit causes the UART to issue an interrupt to the host when the THR interrupt enable is set. The THR bit is set to a logic 1 when the last data byte is transferred from the transmit holding register to the transmit shift register. The bit is reset to logic 0 concurrently with the data loading to the transmit holding register by the host. In the FIFO mode this bit is set when the transmit FIFO is empty, it is cleared when the transmit FIFO contains at least 1 byte. LSR[6]: THR and TSR Empty Flag This bit is set to a logic 1 whenever the transmitter goes idle. It is set to logic 0 whenever either the THR or TSR contains a data character. In the FIFO mode this bit is set to a logic 1 whenever the transmit FIFO and transmit shift register are both empty. LSR[7]: Receive FIFO Data Error Flag
* Logic 0 = No FIFO error (default). * Logic 1 = A global indicator for the sum of all error bits in the RX FIFO. At least one parity error, framing error
or break indication is in the FIFO data. This bit clears when there is no more error(s) in the FIFO. 4.9 Modem Status Register (MSR) - Read Only
This register provides the current state of the modem interface signals, or other peripheral device that the UART is connected. Lower four bits of this register are used to indicate the changed information. These bits are set to a logic 1 whenever a signal from the modem changes state. These bits may be used as general purpose inputs/outputs when they are not used with modem signals.
31
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE MSR[0]: Delta CTS# Input Flag
REV. 1.1.3
* Logic 0 = No change on CTS# input (default). * Logic 1 = The CTS# input has changed state since the last time it was monitored. A modem status interrupt
will be generated if MSR interrupt is enabled (IER bit-3). MSR[1]: Delta DSR# Input Flag
* Logic 0 = No change on DSR# input (default). * Logic 1 = The DSR# input has changed state since the last time it was monitored. A modem status interrupt
will be generated if MSR interrupt is enabled (IER bit-3). MSR[2]: Delta RI# Input Flag
* Logic 0 = No change on RI# input (default). * Logic 1 = The RI# input has changed from a logic 0 to a logic 1, ending of the ringing signal. A modem status
interrupt will be generated if MSR interrupt is enabled (IER bit-3). MSR[3]: Delta CD# Input Flag
* Logic 0 = No change on CD# input (default). * Logic 1 = Indicates that the CD# input has changed state since the last time it was monitored. A modem
status interrupt will be generated if MSR interrupt is enabled (IER bit-3). MSR[4]: CTS Input Status Normally this bit is the compliment of the CTS# input. However in the loopback mode, this bit is equivalent to the RTS# bit in the MCR register. The CTS# input may be used as a general purpose input when the modem interface is not used. MSR[5]: DSR Input Status Normally this bit is the compliment of the DSR# input. In the loopback mode, this bit is equivalent to the DTR# bit in the MCR register. The DSR# input may be used as a general purpose input when the modem interface is not used. MSR[6]: RI Input Status Normally this bit is the compliment of the RI# input. In the loopback mode this bit is equivalent to bit-2 in the MCR register. The RI# input may be used as a general purpose input when the modem interface is not used. MSR[7]: CD Input Status Normally this bit is the compliment of the CD# input. In the loopback mode this bit is equivalent to bit-3 in the MCR register. The CD# input may be used as a general purpose input when the modem interface is not used. 4.10 Scratch Pad Register (SPR) - Read/Write
This is a 8-bit general purpose register for the user to store temporary data. The content of this register is preserved during sleep mode but becomes 0xFF (default) after a reset or a power off-on cycle. 4.11 Baud Rate Generator Registers (DLL and DLM) - Read/Write
The Baud Rate Generator (BRG) is a 16-bit counter that generates the data rate for the transmitter. The rate is programmed through registers DLL and DLM which are only accessible when LCR bit-7 is set to `1'. SEE "PROGRAMMABLE BAUD RATE GENERATOR" ON PAGE 11. for more details. 4.12 Device Identification Register (DVID) - Read Only
This register contains the device ID (0x02 for XR16L2551). Prior to reading this register, DLL and DLM should be set to 0x00.
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XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
4.13
Device Revision Register (DREV) - Read Only
This register contains the device revision information. For example, 0x01 means revision A. Prior to reading this register, DLL and DLM should be set to 0x00. 4.14 Enhanced Feature Register (EFR)
Enhanced features are enabled or disabled using this register. Bit 0-3 provide single or dual consecutive character software flow control selection (see Table 13). When the Xon1 and Xon2 and Xoff1 and Xoff2 modes are selected, the double 8-bit words are concatenated into two sequential characters. Caution: note that whenever changing the TX or RX flow control bits, always reset all bits back to logic 0 (disable) before programming a new setting. EFR[3:0]: Software Flow Control Select Single character and dual sequential characters software flow control is supported. Combinations of software flow control can be selected by programming these bits. TABLE 13: SOFTWARE FLOW CONTROL FUNCTIONS
EFR BIT-3 CONT-3 0 0 1 0 1 X X X 1 EFR BIT-2 CONT-2 0 0 0 1 1 X X X 0 EFR BIT-1 CONT-1 0 X X X X 0 1 0 1 EFR BIT-0 CONT-0 0 X X X X 0 0 1 1 TRANSMIT AND RECEIVE SOFTWARE FLOW CONTROL No TX and RX flow control (default and reset) No transmit flow control Transmit Xon1, Xoff1 Transmit Xon2, Xoff2 Transmit Xon1 and Xon2, Xoff1 and Xoff2 No receive flow control Receiver compares Xon1, Xoff1 Receiver compares Xon2, Xoff2 Transmit Xon1, Xoff1 Receiver compares Xon1 or Xon2, Xoff1 or Xoff2 Transmit Xon2, Xoff2 Receiver compares Xon1 or Xon2, Xoff1 or Xoff2 Transmit Xon1 and Xon2, Xoff1 and Xoff2, Receiver compares Xon1 and Xon2, Xoff1 and Xoff2 No transmit flow control, Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
0
1
1
1
1
1
1
1
0
0
1
1
EFR[4]: Enhanced Function Bits Enable Enhanced function control bit. This bit enables IER bits 4-7, ISR bits 4-5, and MCR bits 5-7 to be modified. After modifying any enhanced bits, EFR bit-4 can be set to a logic 0 to latch the new values. This feature prevents legacy software from altering or overwriting the enhanced functions once set. Normally, it is recommended to leave it enabled, logic 1.
* Logic 0 = modification disable/latch enhanced features. IER bits 4-7, ISR bits 4-5, and MCR bits 5-7 are
saved to retain the user settings. After a reset, the IER bits 4-7, ISR bits 4-5, and MCR bits 5-7are set to a logic 0 to be compatible with ST16C550 mode (default).
* Logic 1 = Enables the above-mentioned register bits to be modified by the user.
33
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE EFR[5]: Special Character Detect Enable
REV. 1.1.3
* Logic 0 = Special Character Detect Disabled (default). * Logic 1 = Special Character Detect Enabled. The UART compares each incoming receive character with
data in Xoff-2 register. If a match exists, the receive data will be transferred to FIFO and ISR bit-4 will be set to indicate detection of the special character. Bit-0 corresponds with the LSB bit of the receive character. If flow control is set for comparing Xon1, Xoff1 (EFR [1:0]= `10') then flow control and special character work normally. However, if flow control is set for comparing Xon2, Xoff2 (EFR[1:0]= `01') then flow control works normally, but Xoff2 will not go to the FIFO, and will generate an Xoff interrupt and a special character interrupt, if enabled via IER bit-5. Special character interrupts are cleared automatically after the next received character. EFR[6]: Auto RTS Flow Control Enable RTS# output may be used for hardware flow control by setting EFR bit-6 to logic 1. When Auto RTS is selected, an interrupt will be generated when the receive FIFO is filled to the programmed trigger level and RTS de-asserts to a logic 1 at the next upper trigger level. RTS# will return to a logic 0 when FIFO data falls below the next lower trigger level. The RTS# output must be asserted (logic 0) before the auto RTS can take effect. RTS# pin will function as a general purpose output when hardware flow control is disabled.
* Logic 0 = Automatic RTS flow control is disabled (default). * Logic 1 = Enable Automatic RTS flow control.
EFR[7]: Auto CTS Flow Control Enable Automatic CTS Flow Control.
* Logic 0 = Automatic CTS flow control is disabled (default). * Logic 1 = Enable Automatic CTS flow control. Data transmission stops when CTS# input de-asserts to logic
1. Data transmission resumes when CTS# returns to a logic 0. 4.15 Software Flow Control Registers (XOFF1, XOFF2, XON1, XON2) - Read/Write
These registers are used as the programmable software flow control characters XOFF1, XOFF2, XON1, and XON2. For more details, see Table 7.
34
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE TABLE 14: UART RESET CONDITIONS FOR CHANNEL A AND B
REGISTERS DLM DLL RHR THR IER FCR ISR LCR MCR LSR MSR RESET STATE Bits 7-0 = 0xXX Bits 7-0 = 0xXX Bits 7-0 = 0xXX Bits 7-0 = 0xXX Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x01 Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x60 Bits 3-0 = Logic 0 Bits 7-4 = Logic levels of the inputs inverted Bits 7-0 = 0xFF Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x00 RESET STATE Logic 1 Logic 1 Logic 1 Logic 1 Logic 1 Logic 0 Three-State Condition
SPR EFR XON1 XON2 XOFF1 XOFF2 I/O SIGNALS TX OP2# RTS# DTR# RXRDY# TXRDY# INT
35
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
REV. 1.1.3
ABSOLUTE MAXIMUM RATINGS
Power Supply Range Voltage at Any Pin Operating Temperature Storage Temperature Package Dissipation 7 Volts GND-0.3 V to +5.5 V -40o to +85oC -65o to +150oC 500 mW
TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: 15%)
Thermal Resistance (48-TQFP) Thermal Resistance (32-QFN) theta-ja =59oC/W, theta-jc = 16oC/W theta-ja = 33oC/W, theta-jc = 22oC/W
ELECTRICAL CHARACTERISTICS
DC ELECTRICAL CHARACTERISTICS Unless otherwise noted: TA=-40o to +85oC, Vcc is 2.25 to 5.5V
SYMBOL VILCK VIHCK VIL VIH VOL PARAMETER Clock Input Low Level Clock Input High Level Input Low Voltage Input High Voltage Output Low Voltage 0.4 0.4 VOH Output High Voltage 2.0 1.8 IIL IIH CIN ICC ISLEEP IPWRSV Input Low Leakage Current Input High Leakage Current Input Pin Capacitance Power Supply Current Sleep Current/ Powersave Current 10 10 5 1 6 10 10 5 1.3 15 10 10 5 3 30 2.4 2.5V LIMITS MIN MAX -0.3 2.0 -0.3 2.0 0.2 5.5 0.6 5.5 3.3V LIMITS MIN MAX -0.3 2.4 -0.3 2.0 0.6 5.5 0.8 5.5 5.0V LIMITS MIN MAX -0.5 3.0 -0.5 2.2 0.6 5.5 0.8 5.5 0.4 UNITS V V V V V V V V V V uA uA pF mA uA See Test 1 IOL = 6 mA IOL = 4 mA IOL = 2 mA IOH = -6 mA IOH = -1 mA IOH = -400 uA CONDITIONS
Test 1: The following inputs must remain steady at VCC or GND state to minimize sleep current: A0-A2, D0-D7, IOR#, IOW# (R/W#), CSA# (CS#), CSB# (A3) and all modem inputs. Also, RXA and RXB inputs must idle at logic 1 state while asleep. Floating inputs may result in sleep currents in the mA range. For Powersave, the UART internally isolates all of these inputs therefore not requiring them to remain steady.
36
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
AC ELECTRICAL CHARACTERISTICS Unless otherwise noted: TA=-40o to +85oC, Vcc is 2.25V to 5.5V, 70 pF load where applicable
SYMBOL PARAMETER MIN CLK OSC TAS TAH TCS TRD TDY TRDV TDD TWR TDY TDS TDH TADS TADH TRWS TRDA TRDH TWDS TWDH TRWH TCSL TCSD TWDO TMOD TRSI Crystal Frequency External Clock Low/High Time External Clock Frequency Address Setup Time (16 Mode) Address Hold Time (16 Mode) Chip Select Width (16 Mode) IOR# Strobe Width (16 Mode) Read Cycle Delay (16 Mode) Data Access Time (16 Mode) Data Disable Time (16 Mode) IOW# Strobe Width (16 Mode) Write Cycle Delay (16 Mode) Data Setup Time (16 Mode) Data Hold Time (16 Mode) Address Setup (68 Mode) Address Hold (68 Mode) R/W# Setup to CS# (68 Mode) Read Data Access (68 mode) Read Data Disable (68 mode) Write Data Setup (68 mode) Write Data Hold (68 Mode) R/W# Hold (68 Mode) CS# Width (68 Mode) CS# Cycle Delay (68 Mode) Delay From IOW# To Output Delay To Set Interrupt From MODEM Input Delay To Reset Interrupt From IOR# 25 15 15 150 150 150 150 150 0 150 150 25 15 10 10 10 125 45 20 10 10 75 75 75 75 75 10 10 150 150 150 125 45 0 75 75 20 10 10 10 10 70 30 15 10 10 50 50 50 50 50 31 16 10 10 75 75 75 70 30 0 50 50 15 10 10 10 10 45 30 LIMITS 2.5 MAX 16 17 30 10 10 50 50 50 45 30 MIN LIMITS 3.3 MAX 20 10 50 MIN LIMITS 5.0 MAX 24 MHz ns MHz ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns UNIT
37
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE AC ELECTRICAL CHARACTERISTICS Unless otherwise noted: TA=-40o to +85oC, Vcc is 2.25V to 5.5V, 70 pF load where applicable
SYMBOL PARAMETER MIN TSSI TRRI TSI TINT TWRI TSSR TRR TWT TSRT TRST N Bclk Delay From Stop To Set Interrupt Delay From IOR# To Reset Interrupt Delay From Stop To Interrupt Delay From Initial INT Reset To Transmit Start Delay From IOW# To Reset Interrupt Delay From Stop To Set RXRDY# Delay From IOR# To Reset RXRDY# Delay From IOW# To Set TXRDY# Delay From Center of Start To Reset TXRDY# Reset Pulse Width Baud Rate Divisor Baud Clock 40 1 216-1 8 LIMITS 2.5 MAX 1 150 150 24 150 1 150 150 8 40 1 216-1 8 MIN LIMITS 3.3 MAX 1 75 75 24 75 1 75 75 8 40 1 216-1 8 MIN LIMITS 5.0 MAX 1 50 50 24 50 1 50 50 8 Bclk ns ns Bclk ns Bclk ns ns Bclk ns Hz UNIT
REV. 1.1.3
16X of data rate
FIGURE 14. CLOCK TIMING
CLK CLK
EXTERNAL CLOCK
OSC
38
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
FIGURE 15. MODEM INPUT/OUTPUT TIMING FOR CHANNELS A & B
IOW # Active T W DO RTS# DTR# Change of state Change of state
CD# CTS# DSR# T MO D INT
Change of state
Change of state
T M OD Active T RSI Active Active
IOR#
Active
Active
Active
T M OD RI# Change of state
FIGURE 16. 16 MODE (INTEL) DATA BUS READ TIMING
A0-A2 TAS
Valid Address TAS
Valid Address
TCS CSA#/ CSB#
TAH
TCS
TAH
TDY TRD IOR# TRD
TRDV D0-D7 Valid Data
TDD
TRDV Valid Data
TDD
RDTm
39
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
REV. 1.1.3
FIGURE 17. 16 MODE (INTEL) DATA BUS WRITE TIMING
A0-A2 TAS
Valid Address TAS
Valid Address
TCS CSA#/ CSB#
TAH
TCS
TAH
TDY TWR IOW# TWR
TDS D0-D7 Valid Data
TDH
TDS Valid Data
TDH
16Write
FIGURE 18. 68 MODE (MOTOROLA) DATA BUS READ TIMING
A0-A3 TADS
Valid Address TCSL TADH
Valid Address
CS# TRWS TCSD
R/W#
TRWH
TRDH TRDA D0-D7 Valid Data Valid Data
68Read
40
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
FIGURE 19. 68 MODE (MOTOROLA) DATA BUS WRITE TIMING
A0-A3 TADS
Valid Address TCSL TADH
Valid Address
CS# TRWS TCSD
R/W#
TRWH
TWDS D0-D7 Valid Data
T WDH Valid Data
68Write
FIGURE 20. RECEIVE READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B
RX
Start Bit Stop Bit TSSR 1 Byte in RHR TSSR
D0:D7
D0:D7 TSSR 1 Byte in RHR TSSR
D0:D7 TSSR 1 Byte in RHR TSSR
INT
RXRDY#
Active Data Ready TRR
Active Data Ready TRR
Active Data Ready TRR
IOR#
(Reading data out of RHR)
RXNFM
41
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE FIGURE 21. TRANSMIT READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B
TX
(Unloading) IER[1] enabled Start Bit Stop Bit
REV. 1.1.3
D0:D7
D0:D7
D0:D7
ISR is read
ISR is read
ISR is read
INT*
TWRI TSRT TWRI TSRT TWRI TSRT
TXRDY#
TWT
TWT
TWT
IOW#
(Loading data into THR)
*INT is cleared when the ISR is read or when data is loaded into the THR.
TXNonFIFO
FIGURE 22. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA DISABLED] FOR CHANNELS A & B
Start Bit
RX
S D0:D7 Stop Bit
S D0:D7 T
D0:D7
TSSI
S D0:D7 T
S D0:D7 T S D0:D7 T
S D0:D7 T
RX FIFO drops below RX Trigger Level
INT
TSSR
RXRDY# First Byte is Received in RX FIFO IOR#
(Reading data out of RX FIFO)
RX FIFO fills up to RX Trigger Level or RX Data Timeout
FIFO Empties
TRRI
TRR
RXINTDMA#
42
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
FIGURE 23. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA ENABLED] FOR CHANNELS A & B
Start Bit Stop Bit
RX
S D0:D7
S D0:D7 T
D0:D7
TSSI
S D0:D7 T
S D0:D7 T S D0:D7 T
S D0:D7 T
RX FIFO drops below RX Trigger Level
INT RX FIFO fills up to RX Trigger Level or RX Data Timeout RXRDY#
TSSR
FIFO Empties
TRRI
TRR
IOR#
(Reading data out of RX FIFO)
RXFIFODMA
FIGURE 24. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE DISABLED] FOR CHANNELS A & B
Start Bit Stop Bit Last Data Byte Transmitted S D0:D7 T S D0:D7 T T S D0:D7 T S D0:D7 T S D0:D7 T TSRT TX FIFO no longer empty
TX FIFO Empty
TX
(Unloading) IER[1] enabled
S D0:D7 T
ISR is read
INT*
TWRI Data in TX FIFO TSI TX FIFO Empty
TXRDY#
TWT
IOW#
(Loading data into FIFO)
*INT is cleared when the ISR is read or when there is at least one character in the FIFO.
TXDMA#
43
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
REV. 1.1.3
FIGURE 25. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE ENABLED] FOR CHANNELS A & B
Start Bit Stop Bit
TX FIFO Empty
Last Data Byte Transmitted S D0:D7 T S D0:D7 T T S D0:D7 T S D0:D7 T S D0:D7 T
TX
(Unloading) IER[1] enabled
S D0:D7 T
ISR is read TX FIFO no longer empty
TSRT TSI
INT*
TWRI
TX FIFO Empty
TXRDY#
TX FIFO Full
At least 1 empty location in FIFO
TWT
IOW#
(Loading data into FIFO)
*INT is cleared when the ISR is read or when there is at least one character in the FIFO.
TXDMA
44
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
PACKAGE DIMENSIONS (48 PIN TQFP - 7 X 7 X 1 mm)
D D1 36 25
37
24
D1
D
48
13
1 B A2 e
1 2
C A Seating Plane A1 L
Note: The control dimension is the millimeter column INCHES SYMBOL A A1 A2 B C D D1 e L a MIN 0.039 0.002 0.037 0.007 0.004 0.346 0.272 MAX 0.047 0.006 0.041 0.011 0.008 0.362 0.280 MILLIMETERS MIN 1.00 0.05 0.95 0.17 0.09 8.80 6.90 MAX 1.20 0.15 1.05 0.27 0.20 9.20 7.10
0.020 BSC 0.018 0 0.030 7
0.50 BSC 0.45 0 0.75 7
45
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
REV. 1.1.3
PACKAGE DIMENSIONS (32 PIN QFN - 5 X 5 X 0.9 mm)
Note: the actual center pad is metallic and the size (D2) is device-dependent with a typical tolerance of 0.3mm
Note: The control dimension is in millimeter. INCHES SYMBOL A A1 A3 D D2 b e L k MIN 0.031 0.000 0.006 0.193 0.138 0.007 MAX 0.039 0.002 0.010 0.201 0.150 0.012 MILLIMETERS MIN 0.80 0.00 0.15 4.90 3.50 0.18 MAX 1.00 0.05 0.25 5.10 3.80 0.30
0.0197 BSC 0.012 0.008 0.020 -
0.50 BSC 0.35 0.20 0.45 -
46
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
REVISION HISTORY
DATE November 2002 March 2003 May 2003 June 2003 July 2003 September 2003 September 2004 May 2005 April 2006 May 2007 REVISION P1.0.0 P1.0.1 P1.0.2 P1.0.3 P1.0.4 1.0.0 1.1.0 1.1.1 1.1.2 1.1.3 Preliminary Datasheet. Updated AC Electrical Characteristics. Updated register set with enhanced features. Added patent number to first page. Added 32 pin QFN package dimensions. Added Device Status to Ordering Information. Updated AC Electrical Characteristics. Final Production Release. Updated 5V tolerance information. Corrected 32-QFN package dimension descriptions. Added GND center pad pin description. Added Device Revision and Device ID registers and descriptions. Updated the Data Access Time (TRDV and TRDA) in AC Electrical Characteristics. Updated the "Voltage at Any Pin" to "GND-0.3 V to +5.5 V." SEE "ABSOLUTE MAXIMUM RATINGS" ON PAGE 36. Updated the QFN package drawing and added the parameter "k". DESCRIPTION
NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user's specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Copyright 2007 EXAR Corporation Datasheet May 2007. Send your UART technical inquiry with technical details to hotline: uarttechsupport@exar.com. Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
47
XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
REV. 1.1.3
TABLE OF CONTENTS
GENERAL DESCRIPTION .................................................................................................1
APPLICATIONS................................................................................................................................................1 FEATURES .....................................................................................................................................................1
FIGURE 1. XR16L2551 BLOCK DIAGRAM ......................................................................................................................................... 1 FIGURE 2. PIN OUT ASSIGNMENT ..................................................................................................................................................... 2 ORDERING INFORMATION.................................................................................................................................2
PIN DESCRIPTIONS .........................................................................................................3
1.0 PRODUCT DESCRIPTION .....................................................................................................................7 2.0 FUNCTIONAL DESCRIPTIONS .............................................................................................................8
2.1 CPU INTERFACE .............................................................................................................................................. 8
FIGURE 3. XR16L2751 TYPICAL INTEL/MOTOROLA DATA BUS INTERCONNECTIONS ........................................................................... 8
2.2 2.3 2.4 2.5
5-VOLT TOLERANT INPUTS ........................................................................................................................... DEVICE RESET ................................................................................................................................................ DEVICE IDENTIFICATION AND REVISION ..................................................................................................... CHANNEL A AND B SELECTION ....................................................................................................................
8 9 9 9
TABLE 1: CHANNEL A AND B SELECT IN 16 MODE ............................................................................................................................ 9 TABLE 2: CHANNEL A AND B SELECT IN 68 MODE ............................................................................................................................ 9
2.6 DMA MODE ....................................................................................................................................................... 9
TABLE 3: TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE........................................................................................... 10
2.7 INTA AND INTB OUTPUTS ............................................................................................................................ 10
TABLE 4: INTA AND INTB PINS OPERATION FOR TRANSMITTER ...................................................................................................... 10 TABLE 5: INTA AND INTB PIN OPERATION FOR RECEIVER ............................................................................................................. 10
2.8 CRYSTAL OSCILLATOR OR EXTERNAL CLOCK INPUT ........................................................................... 10
FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS............................................................................................................................... 11
2.9 PROGRAMMABLE BAUD RATE GENERATOR ........................................................................................... 11
FIGURE 5. EXTERNAL CLOCK CONNECTION FOR EXTENDED DATA RATE .......................................................................................... 11 FIGURE 6. OPERATING FREQUENCY CHART. REQUIRES A 2K OHMS PULL-UP RESISTOR ON XTAL2 PIN TO INCREASE OPERATING SPEED12 TABLE 6: TYPICAL DATA RATES WITH A 14.7456 MHZ CRYSTAL OR EXTERNAL CLOCK ...................................................................... 13
2.10 TRANSMITTER ............................................................................................................................................. 13
2.10.1 2.10.2 2.10.3 FIGURE 7. FIGURE 8. TRANSMIT HOLDING REGISTER (THR) - WRITE ONLY ....................................................................................... 13 TRANSMITTER OPERATION IN NON-FIFO MODE ................................................................................................ 13 TRANSMITTER OPERATION IN FIFO MODE ......................................................................................................... 14 TRANSMITTER OPERATION IN NON-FIFO MODE .............................................................................................................. 14 TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE ..................................................................................... 14
2.11 RECEIVER .................................................................................................................................................... 14
2.11.1 RECEIVE HOLDING REGISTER (RHR) - READ-ONLY .......................................................................................... 15 FIGURE 9. RECEIVER OPERATION IN NON-FIFO MODE .................................................................................................................... 15 FIGURE 10. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE ....................................................................... 15
2.12 AUTO RTS (HARDWARE) FLOW CONTROL ............................................................................................. 16 2.13 AUTO CTS FLOW CONTROL ..................................................................................................................... 16
FIGURE 11. AUTO RTS AND CTS FLOW CONTROL OPERATION....................................................................................................... 17
2.14 AUTO XON/XOFF (SOFTWARE) FLOW CONTROL ................................................................................... 18
TABLE 7: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL ............................................................................................................... 18
2.15 SPECIAL CHARACTER DETECT ............................................................................................................... 18 2.16 INFRARED MODE ........................................................................................................................................ 19
FIGURE 12. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING .......................................................................... 19
2.17
SLEEP MODE WITH AUTO WAKE-UP AND POWERSAVE FEATURE ................................................... 20
2.17.1 SLEEP MODE ........................................................................................................................................................... 20 2.17.2 POWERSAVE FEATURE.......................................................................................................................................... 20
2.18
INTERNAL LOOPBACK .............................................................................................................................. 21
FIGURE 13. INTERNAL LOOP BACK IN CHANNEL A AND B ................................................................................................................ 21
3.0 UART INTERNAL REGISTERS ...........................................................................................................22
TABLE 8: UART CHANNEL A AND B UART INTERNAL REGISTERS...................................................................................... 22 TABLE 9: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1......................................... 23
4.0 INTERNAL REGISTER DESCRIPTIONS .............................................................................................24
4.1 RECEIVE HOLDING REGISTER (RHR) - READ- ONLY ............................................................................... 24 4.2 TRANSMIT HOLDING REGISTER (THR) - WRITE-ONLY ............................................................................ 24 4.3 INTERRUPT ENABLE REGISTER (IER) - READ/WRITE .............................................................................. 24
4.3.1 IER VERSUS RECEIVE FIFO INTERRUPT MODE OPERATION ............................................................................. 24
I
XR16L2551
REV. 1.1.3
LOW VOLTAGE DUART WITH POWERSAVE
4.3.2 IER VERSUS RECEIVE/TRANSMIT FIFO POLLED MODE OPERATION................................................................ 24
4.4 INTERRUPT STATUS REGISTER (ISR) - READ-ONLY ............................................................................... 26
4.4.1 INTERRUPT GENERATION: ...................................................................................................................................... 26 4.4.2 INTERRUPT CLEARING: ........................................................................................................................................... 26 TABLE 10: INTERRUPT SOURCE AND PRIORITY LEVEL ..................................................................................................................... 26
4.5 FIFO CONTROL REGISTER (FCR) - WRITE-ONLY ..................................................................................... 27
TABLE 11: RECEIVE FIFO TRIGGER LEVEL SELECTION ................................................................................................................... 28
4.6 LINE CONTROL REGISTER (LCR) - READ/WRITE ..................................................................................... 28
TABLE 12: PARITY SELECTION ........................................................................................................................................................ 29
4.7 MODEM CONTROL REGISTER (MCR) OR GENERAL PURPOSE OUTPUTS CONTROL - READ/WRITE 4.8 LINE STATUS REGISTER (LSR) - READ ONLY ........................................................................................... 4.9 MODEM STATUS REGISTER (MSR) - READ ONLY .................................................................................... 4.10 SCRATCH PAD REGISTER (SPR) - READ/WRITE .................................................................................... 4.11 BAUD RATE GENERATOR REGISTERS (DLL AND DLM) - READ/WRITE .............................................. 4.12 DEVICE IDENTIFICATION REGISTER (DVID) - READ ONLY .................................................................... 4.13 DEVICE REVISION REGISTER (DREV) - READ ONLY .............................................................................. 4.14 ENHANCED FEATURE REGISTER (EFR) ..................................................................................................
29 30 31 32 32 32 33 33
TABLE 13: SOFTWARE FLOW CONTROL FUNCTIONS ........................................................................................................................ 33
4.15 SOFTWARE FLOW CONTROL REGISTERS (XOFF1, XOFF2, XON1, XON2) - READ/WRITE ................ 34
TABLE 14: UART RESET CONDITIONS FOR CHANNEL A AND B............................................................................................ 35
ABSOLUTE MAXIMUM RATINGS .................................................................................. 36 TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: 15%) 36 ELECTRICAL CHARACTERISTICS................................................................................ 36
DC ELECTRICAL CHARACTERISTICS.............................................................................................................. 36 AC ELECTRICAL CHARACTERISTICS.............................................................................................................. 37
FIGURE 14. FIGURE 16. FIGURE 15. FIGURE 17. FIGURE 18. FIGURE 19. FIGURE 20. FIGURE 21. FIGURE 22. FIGURE 23. FIGURE 24. FIGURE 25. CLOCK TIMING............................................................................................................................................................. 38 16 MODE (INTEL) DATA BUS READ TIMING ................................................................................................................... 39 MODEM INPUT/OUTPUT TIMING FOR CHANNELS A & B ................................................................................................. 39 16 MODE (INTEL) DATA BUS WRITE TIMING ................................................................................................................. 40 68 MODE (MOTOROLA) DATA BUS READ TIMING .......................................................................................................... 40 68 MODE (MOTOROLA) DATA BUS WRITE TIMING......................................................................................................... 41 RECEIVE READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B ......................................................... 41 TRANSMIT READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B ....................................................... 42 RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA DISABLED] FOR CHANNELS A & B........................................ 42 RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA ENABLED] FOR CHANNELS A & B......................................... 43 TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE DISABLED] FOR CHANNELS A & B ........................... 43 TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE ENABLED] FOR CHANNELS A & B ............................ 44
PACKAGE DIMENSIONS (48 PIN TQFP - 7 X 7 X 1 mm)................................................ 45 PACKAGE DIMENSIONS (32 PIN QFN - 5 X 5 X 0.9 mm)............................................... 46
REVISION HISTORY ...................................................................................................................................... 47
TABLE OF CONTENTS ............................................................................................................ I
II

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