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DS28EA00
1-Wire Digital Thermometer with Sequence Detect and PIO
www.maxim-ic.com
GENERAL DESCRIPTION
The DS28EA00 is a digital thermometer with 9-bit (0.5 C) to 12-bit (1/16 C) resolution and alarm function with nonvolatile (NV), user-programmable upper and lower trigger points. Each DS28EA00 has its unique 64-bit registration number that is factoryprogrammed into the chip. Data is transferred serially through the 1-Wire(R) protocol, which requires only one data line and a ground for communication. The improved 1-Wire front end with hysteresis and glitch filter enables the DS28EA00 to perform reliably in large 1-Wire networks. Unlike other 1-Wire thermometers, the DS28EA00 has two additional pins to implement a sequence detect function. This feature allows the user to discover the registration numbers according to the physical device location in a chain, e.g., to measure the temperature in a storage tower at different height. If the sequence detect function is not needed, these pins can be used as generalpurpose input or output. The DS28EA00 can derive the power for its operation directly from the data line ("parasite power"), eliminating the need for an external power supply.
SPECIAL FEATURES
Digital Thermometer Measures Temperatures from -40C to +85C Thermometer Resolution is User-Selectable from 9 to 12 Bits Unique 1-Wire Interface Requires Only One Port Pin for Communication Each Device has a Unique 64-Bit FactoryLasered Registration Number ROM Multidrop Capability Simplifies Distributed Temperature-Sensing Applications Improved 1-Wire Interface with Hysteresis and Glitch Filter User-Definable Nonvolatile (NV) Alarm Threshold Settings/User Bytes Alarm Search Command to Quickly Identify Devices Whose Temperature is Outside of Programmed Limits Standard and Overdrive 1-Wire Speed Two General-Purpose Programmable IO (PIO) Pins Chain Function Sharing the PIO Pins to Detect Physical Sequence of Devices in Network Operating Range: 3.0V to 5.5V, -40C to +85C Can be Powered from Data Line 8-Pin SOP Package
APPLICATIONS
Data Communication Equipment Process Temperature Monitoring HVAC Systems
TYPICAL OPERATING CIRCUIT
VDD 1-Wire Master PX.Y (Microcontroller) #1
VDD IO DS28EA00 PIOB PIOA IO DS28EA00 PIOB PIOA
ORDERING INFORMATION
PART DS28EA00U+ DS28EA00U+T
VDD
#2
VDD
#3
IO DS28EA00 PIOB PIOA
TEMP RANGE -40 to +85C -40 to +85C
PACKAGE 8-pin SOP Tape & Reel
+ Denotes lead-free package.
PIN CONFIGURATION
IO NC +1 2 3 4 8 7 6 5 VDD PIOB PIOA NC
GND
GND
GND
Schematic shows PIOs wired for sequence detect function.
NC GND
Commands, Registers, and Modes are capitalized for clarity.
1-Wire is a registered trademark of Dallas Semiconductor.
8 pin SOP Package Outline Drawing 21-0036
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
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061907
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
ABSOLUTE MAXIMUM RATINGS
IO Voltage to GND IO Sink Current Maximum PIOA or PIOB Pin Current Maximum Current Through GND Pin Operating Temperature Range Junction Temperature Storage Temperature Range Soldering Temperature -0.5V, +6V 20mA 20mA 40mA -40C to +85C +150C -55C to +125C See IPC/JEDEC J-STD-020
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to the absolute maximum rating conditions for extended periods may affect device.
ELECTRICAL CHARACTERISTICS
(TA = -40C to +85C; see Note 1)
PARAMETER Power Supply Supply Voltage Supply Current (Note 5) Standby Current IO Pin General Data 1-Wire Pullup Voltage (Note 2) 1-Wire Pullup Resistance Input Capacitance Input Load Current High-to-Low Switching Threshold Input Low Voltage (Notes 2, 8) Low-to-High Switching Threshold (Notes 5, 6, 9) Switching Hysteresis (Notes 5, 6, 10) Output Low Voltage (Note 11) Recovery Time (Notes 2, 12) SYMBOL VDD IDD IDDS VPUP RPUP CIO IL VTL VIL VTH VHY VOL (Note 2) VDD = 5.5V VDD = 5.5V Local power Parasite power (Notes 2, 3) (Notes 4, 5) IO pin at VPUP (Notes 5, 6, 7) Parasite powered VDD powered (Note 5) Parasite power Parasite power At 4mA 5 2 5 0.5 5.0 Not applicable (0) 65 8 480 48 15 2 1.125 0 60 8 68.1 7.3 640 80 60 6 8.1 1.3 240 24 75 10 s s 1.0 0.21 CONDITIONS MIN 3.0 TYP MAX 5.5 1.5 1.5 VDD 5.5 2.2 1000 1.5 VPUP 1.9V 0.5 0.7 VPUP 1.1V 1.7 0.4 UNITS V mA A V k pF A V V V V V
3.0 3.0 0.3 0.1 0.46
Standard speed, RPUP = 2.2k Overdrive speed, RPUP = 2.2k tREC Overdrive speed, directly prior to reset pulse; RPUP = 2.2k Rising-Edge Hold-Off Time Standard speed tREH (Notes 5, 13) Overdrive speed Timeslot Duration Standard speed tSLOT (Notes 2, 14) Overdrive speed IO Pin, 1-Wire Reset, Presence Detect Cycle Standard speed Reset Low Time (Note 2) tRSTL Overdrive speed Presence-Detect High Standard speed tPDH Time Overdrive speed Presence-Detect Fall Time Standard speed tFPD (Notes 5, 15) Overdrive speed Presence-Detect Low Standard speed tPDL Time Overdrive speed Presence-Detect Sample Standard speed tMSP Time (Notes 2,16) Overdrive speed
s
s s s s s
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
PARAMETER IO Pin, 1-Wire Write Write-0 Low Time (Notes 2, 17) Write-1 Low Time (Notes 2, 17) IO Pin, 1-Wire Read Read Low Time (Notes 2, 18) Read Sample Time (Notes 2, 18) PIO Pins Input Low Voltage Input High Voltage (Note 2) Input Load Current (Note 19) Output Low Voltage (Note 11) Chain-on Pullup Impedance EEPROM Programming Current Programming Time Write/Erase Cycles (Endurance) (Notes 22, 23) Data Retention (Notes 24, 25) Temperature Converter Conversion Current Conversion Time (Note 26) Conversion Error Converter Drift
Note 1: Note 2: Note 3:
SYMBOL tW0L tW1L
CONDITIONS Standard speed Overdrive speed Standard speed Overdrive speed Standard speed Overdrive speed Standard speed Overdrive speed (Note 2) VX = max(VPUP, VDD) Pin at GND At 4mA (Note 5) (Notes 5, 20) (Note 21) At +25C -40C to +85C At +85C (worst case) (Notes 5, 20) 12-bit resolution (1/16C) 11-bit resolution (1/8C) 10-bit resolution (1/4C) 9-bit resolution (1/2C) -10C to +85C below -10C (Note 5) (Note 27)
MIN 60 6 5 1 5 1 tRL + tRL +
TYP
MAX 120 16 15 2 15 - 2- 15 2 0.3
UNITS s s
tRL tMSR VILP VIHP ILP VOLP RCO IPROG tPROG NCY tDR ICONV tCONV D
s s V V A
Vx-1.6 -1.1 0.4 20 40 60 1.5 10 200k 50k 10 1.5 750 375 187.5 93.75 +0.5 +2.0 +0.2
V k mA ms -- years mA ms
-0.5 -0.5 -0.2
C C
Note 4: Note 5: Note 6:
Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: Note 13: Note 14: Note 15: Note 16: Note 17:
Specifications at TA = -40C are guaranteed by design only and not production-tested. System requirement. Maximum allowable pullup resistance is a function of the number of 1-Wire devices in the system and 1-Wire recovery times. The specified value here applies to parasitically powered systems with only one device and with the minimum 1-Wire recovery times. For more heavily loaded systems, local power or an active pullup such as that found in the DS2482-x00, DS2480B, or DS2490 may be required. If longer tREC is used, higher RPUP values may be tolerable. Value is 25pF max. with local power. Maximum value represents the internal parasite capacitance when VPUP is first applied. If RPUP = 2.2k, 2.5s after VPUP has been applied the parasite capacitance will not affect normal communications. Guaranteed by design, characterization, and/or simulation only. Not production tested. VTL, VTH, and VHY are a function of the internal supply voltage, which is itself a function VDD, VPUP, RPUP, 1-Wire timing, and capacitive loading on IO. Lower VDD, VPUP, higher RPUP, shorter tREC, and heavier capacitive loading all lead to lower values of VTL, VTH, and VHY. Voltage below which, during a falling edge on IO, a logic '0' is detected. The voltage on IO needs to be less than or equal to VILMAX at all times the master drives the line to a logic '0'. Voltage above which, during a rising edge on IO, a logic '1' is detected. After VTH is crossed during a rising edge on IO, the voltage on IO has to drop by at least VHY to be detected as logic '0'. The I-V characteristic is linear for voltages less than 1V. Applies to a single parasitically powered DS28EA00 attached to a 1-Wire line. These values also apply to networks of multiple DS28EA00 with local supply. The earliest recognition of a negative edge is possible at tREH after VTH has been reached on the preceding rising edge. Defines maximum possible bit rate. Equal to 1/(tW0L(min) + tREC(min)). Interval during the negative edge on IO at the beginning of a Presence-Detect pulse between the time at which the voltage is 80% of VPUP and the time at which the voltage is 20% of VPUP. Interval after tRSTL during which a bus master is guaranteed to sample a logic '0' on IO if there is a DS28EA00 present. Minimum limit is tPDH(max) + tFPD(max); maximum limit is tPDH(min) + tPDL(min). in Figure 14 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VTH. The actual maximum duration for the master to pull the line low is tW1Lmax + tF - and tW0Lmax + tF - respectively.
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Note 18: Note 19: Note 20: in Figure 14 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input high threshold of the bus master. The actual maximum duration for the master to pull the line low is tRLmax + tF This load current is caused by the internal weak pullup, which asserts a logic '1' to the PIOB and PIOA pins. The logical state of PIOB must not change during the execution of the Conditional Read ROM command. Current drawn from IO during EEPROM programming or temperature conversion interval in parasite powered mode. The pullup circuit on IO during the programming or temperature conversion interval should be such that the voltage at IO is greater than or equal to VPUP(min). If VPUP in the system is close to VPUP(min) then a low impedance bypass of RPUP, which can be activated during programming or temperature conversions may need to be added. The bypass must be activated within 10s from the beginning of the tPROG or tCONV interval, respectively. The tPROG interval begins tREHmax after the trailing rising edge on IO for the last time slot of the command byte for a valid Copy Scratchpad sequence. Interval ends once the device's self-timed EEPROM programming cycle is complete and the current drawn by the device has returned from IPROG to IL (parasite power) or IDDS (local power). Write-cycle endurance is degraded as TA increases. Not 100% production-tested; guaranteed by reliability monitor sampling. Data retention is degraded as TA increases. Guaranteed by 100% production test at elevated temperature for a shorter time; equivalence of this production test to data sheet limit at operating temperature range is established by reliability testing. The tCONV interval begins tREHmax after the trailing rising edge on IO for the last time slot of the command byte for a valid Convert Temperature sequence. Interval ends once the device's self-timed temperature conversion cycle is complete and the current drawn by the device has returned from ICONV to IL (parasite power) or IDDS (local power). Drift data is preliminary and based on a 1000-hour stress test performed on another device with comparable design and fabricated in the same manufacturing process. This test was performed at greater than +85C with VDD = 5.5V. Confirmed thermal drift results for this device are pending the completion of a new 1000-hour stress test.
Note 21:
Note 22: Note 23: Note 24: Note 25: Note 26:
Note 27:
PIN DESCRIPTION
PIN 1 4 2, 3, 5 6 7 8 NAME IO GND N.C. PIOA (DONE\) PIOB (EN\) VDD FUNCTION 1-Wire Bus Interface and Parasitic Power Supply. Open-drain, requires external pullup resistor. Ground Supply No Connection Open-Drain PIOA Channel and Chain Output. For sequence detection, PIOA must be connected to PIOB of the next device in the chain; leave open or tie to GND for the last device in the chain. Open-Drain PIOB Channel and Chain Input. For sequence detection, PIOB of the first device in the chain must be tied to GND. Power Supply Pin. Must be tied to GND for operation in parasite power mode.
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major function blocks of the DS28EA00. The device has three main data components: 1) 64-bit Registration Number, 2) 64-bit scratchpad, and 3) alarm and configuration registers. The 1-Wire ROM Function control unit processes the ROM function commands that allow the device to function in a networked environment. The device function control unit implements the device-specific control functions, such as read/write, temperature conversion, setting the chain state for sequence detection, and PIO access. The CRC generator assists the master verifying data integrity when reading temperatures and memory data. In the sequence detect process, PIOB functions as an input, while PIOA provides the connection to the next device. The power supply sensor allows the master to remotely read whether the DS28EA00 has local power available. Figure 2 shows the hierarchical structure of the 1-Wire protocol. The bus master must first provide one of the eight ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional ("Alarm") Search ROM, 5) Conditional Read ROM, 6) Skip ROM, 7) Overdrive-Skip ROM or 8) Overdrive-Match ROM. Upon completion of an Overdrive ROM command byte executed at standard speed, the device enters Overdrive mode, where all subsequent communication occurs at a higher speed. The protocol required for these ROM function commands is described in Figure 12. After a ROM function command is successfully executed, the device-specific control functions become accessible and the master may provide any one of the nine available commands. The protocol for these control function commands is described in Figure 10. All data is read and written least significant bit first.
Figure 1. DS28EA00 Block Diagram
Internal VDD
VDD
Power Supply Sensor
(ON\)
IO 1-Wire ROM Function Control 64-Bit Registration # PIOB (EN\) Device Function Control 8-Bit CRC Generator Alarm and Config Registers Temperature Sensor PIOA (DONE\) RCO
64-Bit Scratchpad
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
64-BIT REGISTRATION NUMBER
Each DS28EA00 contains a unique Registration Number that is 64 bits long. The first 8 bits are a 1-Wire family code. The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits. See Figure 3 for details. The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in Figure 4. The polynomial is X8 + X5 + X4 + 1. Additional information about the Dallas 1-Wire Cyclic Redundancy Check (CRC) is available in Application Note 27. The shift register bits are initialized to 0. Then starting with the least significant bit of the family code, one bit at a time is shifted in. After the 8th bit of the family code has been entered, then the 48-bit serial number is entered. After the last byte of the serial number has been entered, the shift register contains the CRC value. Shifting in the 8 bits of CRC returns the shift register to all 0s.
Figure 2. Hierachical Structure for 1-Wire Protocol
DS28EA00 Command Level: Available Commands:
Read ROM Match ROM Search ROM Conditional Search ROM Conditional Read ROM Skip ROM Overdrive Skip Overdrive Match
Data Field Affected:
64-bit Reg. # 64-bit Reg. # 64-bit Reg. # 64-bit Reg. #, Temperature Alarm Registers, Scratchpad 64-bit Reg. #, PIOB pin state, Chain state (none) 64-bit Reg. #, OD-Flag 64-bit Reg. #, OD-Flag
1-Wire ROM Function Commands (see Figure 12)
Write Scratchpad Read Scratchpad Copy Scratchpad Device-Specific Control Function Commands (see Figure 10) Convert Temperature Read Power Mode Recall EEPROM PIO Access Read PIO Access Write Chain
Scratchpad Scratchpad Temperature Alarm and Configuration Registers Scratchpad, Temperature Alarm Registers VDD pin voltage Scratchpad, Temperature Alarm and Configuration Registers PIO pins PIO pins Chain state, PIOA pin state
Figure 3. 64-Bit Registration Number
MSB 8-Bit CRC Code MSB LSB MSB 48-Bit Serial Number LSB LSB 8-Bit Family Code (42h) MSB LSB
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Figure 4. 1-Wire CRC Generator
Polynomial = X + X + X + 1
8 5 4
1 STAGE
st
2 STAGE
nd
3 STAGE
rd
4 STAGE
th
5 STAGE
th
6 STAGE
th
7 STAGE
th
8 STAGE
th
X
0
X
1
X
2
X
3
X
4
X
5
X
6
X
7
X
8
INPUT DATA
Memory Description
The memory of the DS28EA00 is shown in Figure 5. It consists of an 8-byte scratchpad and 3 bytes of backup EEPROM. The first two bytes form the temperature readout register, which is updated after a temperature conversion and is read-only. The next 3 bytes are user-writeable; they contain the Temperature High (TH) and the Temperature Low (TL) alarm register and a configuration register. The remaining 3 bytes are "reserved". They power up with constant data and cannot be written by the user. The TH, TL, and configuration register data in the scratchpad control the resolution of a temperature conversion and decide whether a temperature is considered as "alarming". TH, TL, and configuration can be copied to the EEPROM to become nonvolatile (NV). The scratchpad is automatically loaded with EEPROM data when the DS28EA00 powers up.
Figure 5. Memory Map
BYTE ADDRESS 0 1 2 3 4 5 6 7
SCRATCHPAD (POWER-UP STATE) Temperature LSB (50h) Temperature MSB (05h) TH Register or User Byte 1* TL Register or User Byte 2* Configuration Register* Reserved (FFh) Reserved (0Ch) Reserved (10h) <--------> <--------> <-------->
BACKUP EEPROM N/A N/A TH Register or User Byte 1 TL Register or User Byte 2 Configuration Register N/A N/A N/A
*Power-up state depends on value(s) stored in EEPROM.
Register Detailed Description
Temperature Readout Register ADDR 0 1 bit 7 23 S bit 6 22 S bit 5 21 S bit 4 20 S bit 3 2-1 S bit 2 2-2 26 bit 1 2-3 25 bit 0 2-4 24 LS Byte MS Byte
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO The temperature reading is in C using a 16-bit sign-extended two's complement format. Table 1 shows examples of temperature and the corresponding data for 12-bit resolution. With two's complement, the sign bit is set if the value is negative. If the device is configured for 12-bit resolution, all bits in the LS byte are valid; for a reduced resolution, bit 0 (11 bit mode), bits 0 to 1 (10 bit mode), and bits 0 to 2 (9 bit mode) are undefined.
Table 1. Temperature/Data Relationship
TEMPERATURE +85C* +25.0625C +10.125C +0.5C 0C -0.5C -10.125C -25.0625C -40C DIGITAL OUTPUT (BINARY) 0000 0101 0101 0000 0000 0001 1001 0001 0000 0000 1010 0010 0000 0000 0000 1000 0000 0000 0000 0000 1111 1111 1111 1000 1111 1111 0101 1110 1111 1110 0110 1111 1111 1101 1000 0000 DIGITAL OUTPUT (HEX) 0550h 0191h 00A2h 0008h 0000h FFF8h FF5Eh FE6Fh FD80h
*The power-on reset value of the temperature readout register is +85C.
Temperature Alarm Registers ADDR 2 3 bit 7 S S bit 6 26 26 bit 5 25 25 bit 4 24 24 bit 3 23 23 bit 2 22 22 bit 1 21 21 bit 0 20 20 High Alarm (TH) Low Alarm (TL)
The result of a temperature conversion is automatically compared to the values in the alarm registers to determine whether an alarm condition exists. Alarm thresholds are represented as two's complement number. With 8 bits available for sign and value, alarm thresholds can be set in increments of 1C. An alarm condition exists if a temperature conversion results in a value that is either higher than or equal to the value stored in the TH register or lower than or equal to the value stored in the TL register. If a temperature alarm condition exists, the device will respond to the Conditional Search command. The alarm condition is cleared if a subsequent temperature conversion results in a temperature reading within the boundaries defined by the data in the TH and TL registers.
Configuration Register ADDR b7 b6 4 0 R1
b5 R0
b4 1
b3 1
b2 1
b1 1
b0 1
The functional assignments of the individual bits are explained in the table below. Bits 0 to 4 and bit 7 have no function; they cannot be changed by the user. As a factory default, the device operates in 12-bit resolution. BIT DESCRIPTION R0, R1: Temperature Converter Resolution BIT(S) b5, b6 DEFINITION These bits control the resolution of the temperature converter. The codes are as follows: R1 R0 0 0 9 bits 0 1 10 bits 1 0 11 bits 1 1 12 bits
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
PIO Structure
Each PIO consists of an open-drain pulldown transistor and an input path to read the pin state. The transistor is controlled by the PIO Output Latch, as shown in Figure 6. The Device Function Control unit connects the PIOs logically to the 1-Wire interface. PIOA has a pullup path to internal VDD to facilitate the sequence detect function (see Figure 1) in conjunction with the Chain command; PIOB is truely an open-drain structure. The power-on default state of the PIO output transistors is off; high-impedance on-chip resistors (not shown in the graphic) pull the PIO pins to internal VDD.
Figure 6. PIO Simplified Logic Diagram
PIO Pin State PIO Output Latch State. PIO Data PIO Clock CLOCK D Q Q PIO Output Latch PIO Pin
Chain Function
The chain function is a feature that allows the 1-Wire master to discover the physical sequence of devices that are wired as a linear network ("chain"). This is particularly convenient for devices that are installed at equal spacing along a long cable, e.g., to measure temperatures at different locations inside a storage tower or tank. Without chain function, the master needs a lookup table to correlate registration number to the physical location. The chain function requires two pins, an input (EN\) to enable a device to respond during the discovery and an output (DONE\) to inform the next device in the chain that the discovery of its neighbor is done. The two general purpose ports of the DS28EA00 are re-used for the chain function. PIOB functions as EN\ input and PIOA generates the DONE\ signal, which is connected to the EN\ input of the next device, as shown in the typical operating circuit on page 1. The EN\ input of the first device in the chain needs to be hardwired to GND or logic `0' must be applied for the duration of the sequence discovery process. Besides the two pins, the sequence discovery relies on the Conditional Read ROM command. For the chain function and normal PIO operation to coexist, the DS28EA00 distinguishes three chain states, OFF, ON, and DONE. The transition from one chain state to another is controlled through the Chain command. Table 2 summarizes the chain states and the specific behavior of the PIO pins.
Table 2. Chain States
CHAIN STATE OFF (default) ON DONE DEVICE BEHAVIOR PIOB (EN\) PIO (high impedance) EN\ input No function PIOA (DONE\) PIO (high impedance) Pullup on Pulldown on (DO\ logic `0') Conditional Read ROM Not recognized Recognized if EN\ is `0' Not recognized
The power-on default chain state is OFF, where PIOA and PIOB are solely controlled through the PIO Access Read and Write commands. In the chain ON state PIOA is pulled high to the device's internal VDD supply through a ~40k resistor, applying a logic `1' to the PIOB (EN\) pin of the next device. Only in the ON state does a DS28EA00 respond to the Conditional Read ROM command, provided its EN\ is at logic `0'. After a device's ROM 9 of 29
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO Registration number is read, it is put into the chain DONE state, which enables the next device in the chain to respond to the Conditional Read ROM command. At the beginning of the sequence discovery process all devices are put into the chain ON state. As the discovery progresses, one device after another is transitioned into the DONE state until all devices are identified. Finally, all devices are put into the chain OFF state, which releases the PIOs and restores their power-on default state.
CONTROL FUNCTION COMMANDS
The Control Function Flow Chart (Figure 10) describes the protocols necessary for measuring temperatures, accessing the memory and PIOs, and changing the chain state. Examples on how to use these and other functions are included at the end of this document. The communication between master and DS28EA00 takes place either at standard speed (default, OD = 0) or at Overdrive Speed (OD = 1). If not explicitly set into the Overdrive mode after power-up the DS28EA00 communicates at standard speed.
WRITE SCRATCHPAD [4Eh]
This command allows the master to write 3 bytes of data to the scratchpad of the DS28EA00. The first data byte is associated with the TH register (byte address 2), the second byte is associated with the TL register (byte address 3), and the third byte is associated with the configuration register (byte address 4). Data must be transmitted least significant bit first. All three bytes MUST be written before the master issues a reset, or the data may be corrupted.
READ SCRATCHPAD [BEh]
This command allows the master to read the contents of the scratchpad. The data transfer starts with the least significant bit of the temperature readout register at byte address 0 and continues through the remaining 7 bytes of the scratchpad. If the master continues reading, it gets a 9th byte, which is an 8-bit CRC of all the data in the scratchpad. This CRC is generated by the DS28EA00 and uses the same polynomial function as is used with the ROM Registration Number. The CRC is transmitted in its true (non-inverted) form. The master may issue a reset to terminate the reading early if only part of the scratchpad data is needed.
COPY SCRATCHPAD [48h]
This command copies the contents of the scratchpad byte addresses 2 to 4 (TH, TL and configuration registers) to the back-up EEPROM. If the device has no VDD power, the master must enable a strong pullup on the 1-Wire bus for the duration of tPROGMAX within 10s after this command is issued. If the device is powered through the VDD pin, the master may generate read time slots to monitor the copy process. Copy is completed when the master reads 1bits instead of 0-bits.
CONVERT TEMPERATURE [44h]
This command initiates a temperature conversion. Following the conversion, the resulting thermal data is found in the temperature readout register in the scratchpad and the DS28EA00 returns to its low-power idle state. If the device has no VDD power, the master must enable a strong pullup on the 1-Wire bus for the duration of the applicable resolution-dependent tCONVMAX within 10s after this command is issued. If the device is powered through the VDD pin, the master may generate read time slots to monitor the conversion process. The conversion is completed when the master reads 1-bits instead of 0-bits.
READ POWER MODE [B4h]
For Copy Scratchpad and Convert Temperature the master needs to know whether the DS28EA00 has VDD power available. The Read Power Mode command is implemented to provide the master with this information. After the command code, the master issues read time slots. If the master reads 1's, the device is powered through the VDD pin. If the device is powered through the 1-Wire line, the master will read 0's. The power supply sensor samples the state of the VDD pin for every time slot that the master generates after the command code.
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
RECALL EEPROM [B8h]
This command recalls the TH and TL alarm trigger values and configuration data from backup EEPROM into their respective locations in the scratchpad. After having transmitted the command code, the master may issue read time slots to monitor the completion of the recall process. Recall is completed when the master reads 1-bits instead of 0-bits. The recall occurs automatically at power-up, not requiring any activity by the master.
PIO ACCESS READ [F5h]
This command reads the PIO logical status and reports it together with the state of the PIO Output Latch in an endless loop. A PIO Access Read can be terminated at any time with a 1-Wire Reset. PIO Access Read can be executed in the Chain ON and Chain DONE state. While the device is in Chain ON or Chain DONE state, the PIO output latch states will always read out as 1s; the PIO pin state may not be reported correctly. PIO Status Bit Assignment b7 b6 b5 b4 b3 PIOB Output Latch State b2 PIOB Pin State b1 PIOA Output Latch State b0 PIOA Pin State
Complement of b3 to b0
The state of both PIO channels is sampled at the same time. The first sampling occurs during the last (most significant) bit of the command code F5h. The PIO status is then reported to the bus master. While the master receives the last (most significant) bit of the PIO status byte, the next sampling occurs and so on until the master generates a 1-Wire Reset. The sampling occurs with a delay of tREH+x from the rising edge of the MS bit of the previous byte, as shown in Figure 7. The value of "x" is approximately 0.2s.
Figure 7. PIO Access Read Timing Diagram
MS 2 bits of previous byte VTH IO tREH+x Sampling Point LS 2 bits of PIO Status byte
Notes: 1 The "previous byte" could be the command code or the data byte resulting from the previous PIO sample. 2 The sample point timing also applies to the PIO Access Write command, with the "previous byte" being the write confirmation byte (AAh).
PIO ACCESS WRITE [A5h]
The PIO Access Write command writes to the PIO output latches, which control the pulldown transistors of the PIO channels. In an endless loop this command first writes new data to the PIO and then reads back the PIO status. This implicit read-after-write can be used by the master for status verification. A PIO Access Write can be terminated at any time with a 1-Wire Reset. The PIO Access Write command is ignored by the device while in Chain ON or Chain DONE state. PIO Output Data Bit Assignment b7 b6 b5 b4 X X X X
b3 X
b2 X
b1 PIOB
b0 PIOA
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO After the command code the master transmits a PIO Output Data byte that determines the new state of the PIO output transistors. The first (least significant) bit is associated to PIOA; the next bit affects PIOB. The other 6 bits of the new state byte do not have corresponding PIO pins. These bits should always be transmitted as "1"s. To switch the output transistor on, the corresponding bit value is 0. To switch the output transistor off (non-conducting) the bit must be 1. This way the bit transmitted as the new PIO output state arrives in its true form at the PIO pin. To protect the transmission against data errors, the master must repeat the PIO Output Data byte in its inverted form. Only if the transmission was error-free will the PIO status change. The actual PIO transition to the new state occurs with a delay of tREH + x from the rising edge of the MS bit of the inverted PIO byte, as shown in Figure 8. The value of "x" is approximately 0.2s. To inform the master about the successful communication of the PIO byte, the DS28EA00 transmits a confirmation byte with the data pattern AAh. While the MS bit of the confirmation byte is transmitted, the DS28EA00 samples the state of the PIO pins, as shown in Figure 7, and sends it to the master. The master can either continue writing more data to the PIO or issue a 1-Wire Reset to end the command.
Figure 8. PIO Access Write Timing Diagram
MS 2 bits of inverted PIO Output Data byte IO VTH tREH+x PIO LS 2 bits of confirmation byte (AAh)
CHAIN COMMAND [99h]
This command allows the master to put the DS28EA00 into one of the three Chain States, as shown in Figure 9. The device powers up in the Chain OFF state. To transition a DS28EA00 from one state to another, the master must send a suitable Chain Control byte after the Chain Command code. Only the codes 3Ch, 5Ah and 96h (true form) are valid, assigned to OFF, ON, and DONE, in this sequence. This control byte is first transmitted in its true form and then in its inverted form. If the Chain state change was successful, the master receives AAh confirmation bytes. If the change was not successful (control byte transmission error, invalid control byte) the master will read 00h bytes instead.
Figure 9. Chain State Transition Diagram
Power-on Reset (POR)
OFF
Chain DONE
Chain ON
Chain OFF or POR Chain DONE
ON
Chain ON These transitions are permissible, but do not occur during normal operation.
DONE
12 of 29
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Figure 10-1. Control Function Flow Chart
Bus Master TX Control Function Command 4Eh Write Scratchpad? Y From ROM Functions Flow Chart (Figure 12) BEh Read Scratchpad? Y DS28EA00 sets byte address = 0 To Figure 10 nd 2 Part
N
N
DS28EA00 sets byte address = 2
Master RX byte from scratchpad Master TX data byte to scratchpad Master TX Reset? Master TX Reset? N Y N Byte Address = 7? N Byte Address = 4? N Y DS28EA00 increments byte address Y Y
DS28EA00 increments byte address
Master RX 8-bit CRC of data
Master TX Reset? N N Master RX "1s" Master TX Reset? Y
Y
To ROM Functions Flow Chart (Figure 12)
From Figure 10 nd 2 Part
13 of 29
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Figure 10-2. Control Function Flow Chart (continued)
From Figure 10 st 1 Part
48h Copy Scratchpad? Y
N Master decision. The master needs to know whether VDD power is available. N
44h Convert Temperature Y
To Figure 10 N 3rd Part
Y
VDD Powered?
Y
VDD Powered?
N
DS28EA00 starts copy to EEPROM
Master activates strong pull-up for tPROG Y
DS28EA00 starts Temperature Conversion
Master activates strong pull-up for tCONV Y
Copy Completed? N Master RX "0s"
DS28EA00 copies scratchpad data to EEPROM
Conversion Completed? N
DS28EA00 converts Temperature
Master deactivates strong pull-up
Master RX "0s"
Master deactivates strong pull-up
Master TX Reset? N Master RX "1s"
Y
Master TX Reset? N Master RX "1s"
Y
To Figure 10 st 1 Part
From Figure 10 rd 3 Part
14 of 29
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Figure 10-3. Control Function Flow Chart (continued)
From Figure 10 nd 2 Part
B4h Read Power Mode? Y
N
B8h Recall EEPROM? Y
N
To Figure 10 th 4 Part
Y
VDD Powered?
N
DS28EA00 starts Recall EEPROM to Scratchpad
Master RX "1s"
Master RX "0s" Recall Completed? N Master RX "0s"
Y
Master RX "1s"
Master TX Reset? N
Y Master TX Reset? N Master RX "1s" Y
To Figure 10 nd 2 Part
From Figure 10 th 4 Part
15 of 29
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Figure 10-4. Control Function Flow Chart (continued)
From Figure 10 rd 3 Part
F5h PIO Access Read? Y
N
A5h PIO Access Write? Y Bus Master TX new PIO Output Data Byte Bus Master TX inverted new PIO Output Data Byte
N
To Figure 10 th 5 Part
Note 1) See the command description for the exact timing of the PIO pin sampling and updating.
N Transmission OK? Y DS28EA00 Samples PIO Pin 1) DS28EA00 Updates PIO Bus Master RX Confirmation AAh Bus Master RX "1"s Master TX Reset? Bus Master RX PIO Pin Status DS28EA00 Samples PIO Pin Bus Master RX PIO Pin Status 1) Y N 1)
Master TX Reset? Y
N
N
Master TX Reset? Y
Y To Figure 10 rd 3 Part From Figure 10 th 5 Part
16 of 29
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Figure 10-5. Control Function Flow Chart (continued)
From Figure 10 th 4 Part
99h Chain Command? Y Master TX Chain Control Byte
N
Master TX Reset? Error defined as: repeated control byte not equal to inverted control byte Y N Master RX "1s"
Y
Master TX Inverted Chain Control Byte
Transmission Error? N
Control Byte Valid? Valid Chain Control Byte Codes: 3Ch 5Ah 96h Off On Done DS28EA00 updates chain state Y
N
Master RX confirmation code AAh
Master RX inverted chain control byte
Master RX error code 00h
N
Master TX Reset? Y
N
Master TX Reset? Y
N
Master TX Reset? Y
To Figure 10 th 4 Part
17 of 29
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
1-Wire BUS SYSTEM
The 1-Wire bus is a system that has a single bus master and one or more slaves. In all instances the DS28EA00 is a slave device. The bus master is typically a microcontroller. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). The 1-Wire protocol defines bus transactions in terms of the bus state during specific time slots, which are initiated on the falling edge of sync pulses from the bus master.
HARDWARE CONFIGURATION
The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open-drain or tri-state outputs. The 1-Wire port of the DS28EA00 is open drain with an internal circuit equivalent to that shown in Figure 11. A multidrop bus consists of a 1-Wire bus with multiple slaves attached. The DS28EA00 supports both a Standard and Overdrive communication speed of 15.3kbps (max) and 125kbps (max), respectively. Note that legacy 1-Wire products support a standard communication speed of 16.3kbps and Overdrive of 142kbps. The slightly reduced rates for the DS28EA00 are a result of additional recovery times, which in turn were driven by a 1-Wire physical interface enhancement to improve noise immunity. The value of the pullup resistor primarily depends on the network size and load conditions. The DS28EA00 requires a pullup resistor of 2.2k (max) at any speed. The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus MUST be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low for more than 16s (Overdrive speed) or more than 120s (standard speed), one or more devices on the bus may be reset.
Figure 11. Hardware Configuration
BUS MASTER VPUP RPUP RX DATA RX TX DS28EA00 1-Wire PORT
TX Open-Drain Port Pin
IL RX = RECEIVE TX = TRANSMIT 100 MOSFET
TRANSACTION SEQUENCE
The protocol for accessing the DS28EA00 through the 1-Wire port is as follows: Initialization ROM Function Command Control Function Command Transaction/Data
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that the DS28EA00 is on the bus and is ready to operate. For more details, see the 1-Wire Signaling section. 18 of 29
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
1-Wire ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the eight ROM function commands that the DS28EA00 supports. All ROM function commands are 8 bits long. A list of these commands follows (refer to the flow chart in Figure 12).
READ ROM [33h]
This command allows the bus master to read the DS28EA00's 8-bit family code, unique 48-bit serial number, and 8-bit CRC. This command can only be used if there is a single slave on the bus. If more than one slave is present on the bus, a data collision occurs when all slaves try to transmit at the same time (open drain produces a wiredAND result). The resultant family code and 48-bit serial number result in a mismatch of the CRC.
MATCH ROM [55h]
The Match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a specific DS28EA00 on a multidrop bus. Only the DS28EA00 that exactly matches the 64-bit ROM sequence responds to the following Control Function command. All other slaves wait for a reset pulse. This command can be used with a single or multiple devices on the bus.
SEARCH ROM [F0h]
When a system is initially brought up, the bus master might not know the number of devices on the 1-Wire bus or their registration numbers. By taking advantage of the wired-AND property of the bus, the master can use a process of elimination to identify the registration numbers of all slave devices. For each bit of the registration number, starting with the least significant bit, the bus master issues a triplet of time slots. On the first slot, each slave device participating in the search outputs the true value of its registration number bit. On the second slot, each slave device participating in the search outputs the complemented value of its registration number bit. On the third slot, the master writes the true value of the bit to be selected. All slave devices that do not match the bit written by the master stop participating in the search. If both of the read bits are zero, the master knows that slave devices exist with both states of the bit. By choosing which state to write, the bus master branches in the ROM code tree. After one complete pass, the bus master knows the registration number of a single device. Additional passes identify the registration numbers of the remaining devices. Refer to Application Note 187: 1-Wire Search Algorithm for a detailed discussion, including an example. The Search ROM command does not reveal any information about the location of a device in a network. If multiple DS28EA00 are wired as a linear network ("chain"), the device location can be detected using Conditional Read ROM in conjunction with the Chain function.
CONDITIONAL SEARCH ROM [ECh]
The Conditional Search ROM command operates similarly to the Search ROM command except that only those devices, which fulfill certain conditions, participates in the search. This function provides an efficient means for the bus master to identify devices on a multidrop system that have to signal an important event. After each pass of the conditional search that successfully determined the 64-bit ROM code for a specific device on the multidrop bus, that particular device can be individually accessed as if a Match ROM had been issued, since all other devices will have dropped out of the search process and will be waiting for a reset pulse. The DS28EA00 will respond to the conditional search if a temperature alarm condition exists. For more details see Temperature Alarm Registers.
CONDITIONAL READ ROM [0Fh]
This command is used in conjunction with the Chain function to detect the physical sequence of devices in a linear network ("chain"). A DS28EA00 responds to Conditional Read ROM if two conditions are met: a) the device is in chain ON state, and b) the EN\ input (PIOB) is at logic `0'. This condition is met by exactly one device during the sequence discovery process. Upon receiving the Conditional Read ROM command, this particular device transmits its 64-bit registration numberA device in chain ON state, but with a logic `1' level at EN\ does not respond to Conditional Read ROM. See Sequence Discovery Procedure for more details on the use of Conditional Read ROM and the Chain command.
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
SKIP ROM [CCh]
This command can save time in a single-drop bus system by allowing the bus master to access the control functions without providing the 64-bit ROM code. If more than one slave is present on the bus and, for example, a read command is issued following the Skip ROM command, data collision occurs on the bus as multiple slaves transmit simultaneously (open-drain pulldowns produce a wired-AND result).
OVERDRIVE SKIP ROM [3Ch]
On a single-drop bus this command can save time by allowing the bus master to access the control functions without providing the 64-bit ROM code. Unlike the normal Skip ROM command, the Overdrive Skip ROM sets the DS28EA00 in the Overdrive mode (OD = 1). All communication following this command has to occur at Overdrive speed until a reset pulse of minimum 480s duration resets all devices on the bus to standard speed (OD = 0). When issued on a multidrop bus, this command sets all Overdrive-supporting devices into Overdrive mode. To subsequently address a specific Overdrive-supporting device, a reset pulse at Overdrive speed has to be issued followed by a Match ROM or Search ROM command sequence. This speeds up the time for the search process. If more than one slave supporting Overdrive is present on the bus and the Overdrive Skip ROM command is followed by a Read command, data collision occurs on the bus as multiple slaves transmit simultaneously (open-drain pulldowns produce a wired-AND result).
OVERDRIVE MATCH ROM [69h]
The Overdrive Match ROM command followed by a 64-bit ROM sequence transmitted at Overdrive Speed allows the bus master to address a specific DS28EA00 on a multidrop bus and to simultaneously set it in Overdrive mode. Only the DS28EA00 that exactly matches the 64-bit ROM sequence responds to the subsequent control function command. Slaves already in Overdrive mode from a previous Overdrive Skip or successful Overdrive Match command remain in Overdrive mode. All overdrive-capable slaves return to standard speed at the next Reset Pulse of minimum 480s duration. The Overdrive Match ROM command can be used with a single or multiple devices on the bus.
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Figure 12-1. ROM Funtions Flow Chart
From Control Functions Flow Chart (Figure 10) Bus Master TX Reset Pulse OD Reset Pulse? Y Bus Master TX ROM Function Command 33h Read ROM Command? Y N DS28EA00 TX Presence Pulse 55h Match ROM Command? Y N F0h Search ROM Command? Y N N OD = 0 From Figure 12, 2
nd
Part
To Figure 12 nd 2 Part ECh Cond. Search Command? Y
N
N Temp. Alarm? Y DS28EA00 TX Family Code (1 Byte) Master TX Bit 0
DS28EA00 TX Bit 0 DS28EA00 TX Bit 0 Master TX Bit 0 DS28EA00 TX Bit 0 DS28EA00 TX Bit 0 Master TX Bit 0
Bit 0 Match? Y DS28EA00 TX Serial Number (6 Bytes) Master TX Bit 1
N
N
Bit 0 Match? Y
DS28EA00 TX Bit 1 DS28EA00 TX Bit 1 Master TX Bit 1
N
Bit 0 Match? Y
DS28EA00 TX Bit 1 DS28EA00 TX Bit 1 Master TX Bit 1
Bit 1 Match? Y DS28EA00 TX CRC Byte
N
N
Bit 1 Match? Y
DS28EA00 TX Bit 63 DS28EA00 TX Bit 63 Master TX Bit 63
N
Bit 1 Match? Y
DS28EA00 TX Bit 63 DS28EA00 TX Bit 63 Master TX Bit 63
Master TX Bit 63
Bit 63 Match? Y
N
N
Bit 63 Match? Y
N
Bit 63 Match? Y To Figure 12 nd 2 Part From Figure 12 nd 2 Part
To Control Functions Flow Chart (Figure 10)
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Figure 12-2. ROM Functions Flow Chart
To Figure 12, 1 Part
st
From Figure 12 st 1 Part 0Fh Cond. Read ROM? Y N CCh Skip ROM Cmnd.? Y N 3Ch OD Skip ROM? Y N 69h OD Match ROM? Y N
OD = 1
OD = 1
N
Chain = ON?
Master TX Bit 0 1) OD = 0
Y N
EN\ = LOW?
Master TX Reset ?
Y
Bit 0 Match? Y Master TX Bit 1
N
N Y DS28EA00 TX Family Code (1 Byte) DS28EA00 TX Serial Number (6 Bytes) DS28EA00 TX CRC Byte Bit 63 Match? Y From Figure 12 st 1 Part To Figure 12 st 1 Part Y
Master TX Reset?
Bit 1 Match? Y
N
1) OD = 0
N
Master TX Bit 63 1) OD = 0
N
1) The OD flag remains at 1 if the device was already at Overdrive speed before the Overdrive Match ROM command was issued.
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
1-Wire SIGNALING
The DS28EA00 requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write-Zero, Write-One, and Read-Data. Except for the Presence pulse, the bus master initiates all falling edges. The DS28EA00 can communicate at two different speeds, standard speed, and Overdrive Speed. If not explicitly set into the Overdrive mode, the DS28EA00 communicates at standard speed. While in Overdrive Mode the fast timing applies to all waveforms. To get from idle to active, the voltage on the 1-Wire line needs to fall from VPUP below the threshold VTL. To get from active to idle, the voltage needs to rise from VILMAX past the threshold VTH. The time it takes for the voltage to make this rise is seen in Figure 13 as '' and its duration depends on the pullup resistor (RPUP) used and the capacitance of the 1-Wire network attached. The voltage VILMAX is relevant for the DS28EA00 when determining a logical level, not triggering any events. Figure 13 shows the initialization sequence required to begin any communication with the DS28EA00. A Reset Pulse followed by a Presence Pulse indicates the DS28EA00 is ready to receive data, given the correct ROM and Control Function command. If the bus master uses slew-rate control on the falling edge, it must pull down the line for tRSTL + tF to compensate for the edge. A tRSTL duration of 480s or longer exits the Overdrive Mode, returning the device to standard speed. If the DS28EA00 is in Overdrive Mode and tRSTL is no longer than 80s, the device remains in Overdrive Mode. If the device is in Overdrive Mode and tRSTL is between 80s and 480s, the device will reset, but the communication speed is undetermined.
Figure 13. Initialization Procedure "Reset and Presence Pulses"
MASTER TX "RESET PULSE" MASTER RX "PRESENCE PULSE" VPUP VIHMASTER VTH VTL VILMAX 0V tF tRSTL tPDH MASTER tPDL tRSTH tREC DS28EA00 tMSP
RESISTOR
After the bus master has released the line it goes into receive mode. Now the 1-Wire bus is pulled to VPUP through the pullup resistor, or in case of a DS2482-x00 or DS2480B driver, by active circuitry. When the threshold VTH is crossed, the DS28EA00 waits for tPDH and then transmits a Presence Pulse by pulling the line low for tPDL. To detect a presence pulse, the master must test the logical state of the 1-Wire line at tMSP. The tRSTH window must be at least the sum of tPDHMAX, tPDLMAX, and tRECMIN. Immediately after tRSTH is expired, the DS28EA00 is ready for data communication. In a mixed population network, tRSTH should be extended to minimum 480s at standard speed and 48s at Overdrive speed to accommodate other 1-Wire devices.
READ/WRITE TIME SLOTS
Data communication with the DS28EA00 takes place in time slots, which carry a single bit each. Write-time slots transport data from bus master to slave. Read-time slots transfer data from slave to master. Figure 14 illustrates the definitions of the write- and read-time slots. All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line falls below the threshold VTL, the DS28EA00 starts its internal timing generator that determines when the data line is sampled during a write-time slot and how long data is valid during a read-time slot.
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
Master-To-Slave
For a write-one time slot, the voltage on the data line must have crossed the VTH threshold before the write-one low time tW1LMAX is expired. For a write-zero time slot, the voltage on the data line must stay below the VTH threshold until the write-zero low time tW0LMIN is expired. For the most reliable communication, the voltage on the data line should not exceed VILMAX during the entire tW0L or tW1L window. After the VTH threshold has been crossed, the DS28EA00 needs a recovery time tREC before it is ready for the next time slot.
Figure 14. Read/Write Timing Diagram Write-One Time Slot
VPUP VIHMASTER VTH VTL VILMAX 0V tF tW1L
RESISTOR
tSLOT MASTER
Write-Zero Time Slot
VPUP VIHMASTER VTH VTL VILMAX 0V tF RESISTOR tSLOT MASTER tW0L
tREC
Read-Data Time Slot
VPUP VIHMASTER VTH VTL VILMAX 0V tF RESISTOR tSLOT MASTER DS28EA00 tRL tMSR Master Sampling Window tREC
Slave-To-Master
A read-data time slot begins like a write-one time slot. The voltage on the data line must remain below VTL until the read low time tRL is expired. During the tRL window, when responding with a 0, the DS28EA00 starts pulling the data line low; its internal timing generator determines when this pulldown ends and the voltage starts rising again. When responding with a 1, the DS28EA00 does not hold the data line low at all, and the voltage starts rising as soon as tRL is over. 24 of 29
DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO The sum of tRL + (rise time) on one side and the internal timing generator of the DS28EA00 on the other side define the master sampling window (tMSRMIN to tMSRMAX) in which the master must perform a read from the data line. For the most reliable communication, tRL should be as short as permissible, and the master should read close to but no later than tMSRMAX. After reading from the data line, the master must wait until tSLOT is expired. This guarantees sufficient recovery time tREC for the DS28EA00 to get ready for the next time slot. Note that tREC specified herein applies only to a single DS28EA00 attached to a 1-Wire line. For multidevice configurations, tREC needs to be extended to accommodate the additional 1-Wire device input capacitance. Alternatively, an interface that performs active pullup during the 1-Wire recovery time such as the DS2482-x00 or DS2480B 1-Wire line drivers can be used.
IMPROVED NETWORK BEHAVIOR (SWITCHPOINT HYSTERESIS)
In a 1-Wire environment, line termination is possible only during transients controlled by the bus master (1-Wire driver). 1-Wire networks, therefore, are susceptible to noise of various origins. Depending on the physical size and topology of the network, reflections from end points and branch points can add up, or cancel each other to some extent. Such reflections are visible as glitches or ringing on the 1-Wire communication line. Noise coupled onto the 1-Wire line from external sources can also result in signal glitching. A glitch during the rising edge of a time slot can cause a slave device to lose synchronization with the master and, consequently, result in a search ROM command coming to a dead end or cause a device-specific function command to abort. For better performance in network applications, the DS28EA00 uses a new 1-Wire front end, which makes it less sensitive to noise and also reduces the magnitude of noise injected by the slave device itself.. The 1-Wire front end of the DS28EA00 differs from traditional slave devices in four characteristics. 1) The falling edge of the presence pulse has a controlled slew rate. This provides a better match to the line impedance than a digitally switched transistor, converting the high frequency ringing known from traditional devices into a smoother low-bandwidth transition. The slew rate control is specified by the parameter tFPD, which has different values for standard and Overdrive speed. 2) There is additional low-pass filtering in the circuit that detects the falling edge at the beginning of a time slot. This reduces the sensitivity to high-frequency noise. This additional filtering does not apply at Overdrive speed. 3) There is a hysteresis at the low-to-high switching threshold VTH. If a negative glitch crosses VTH but does not go below VTH - VHY, it will not be recognized (Figure 15, Case A). The hysteresis is effective at any 1-Wire speed. 4) There is a time window specified by the rising edge hold-off time tREH during which glitches are ignored, even if they extend below VTH - VHY threshold (Figure 15, Case B, tGL < tREH). Deep voltage droops or glitches that appear late after crossing the VTH threshold and extend beyond the tREH window cannot be filtered out and are taken as the beginning of a new time slot (Figure 15, Case C, tGL tREH). Devices that have the parameters VHY, and tREH specified in their electrical characteristics use the improved 1-Wire front end.
Figure 15. Noise Suppression Scheme
VPUP VTH VHY Case A 0V tGL tGL Case B Case C tREH tREH
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
SEQUENCE DISCOVERY PROCEDURE
Precondition: The PIOB pin (EN\) of the first device in the chain is at logic 0. The PIOA pin (DONE\) of the first device connects to the PIOB of the second device in the chain, etc., as shown in Figure 16. The 1-Wire master detects the physical sequence of the devices in the chain by performing the following procedure: Starting Condition: The master issues a Skip ROM command followed by a Chain ON command, which puts all devices in the Chain ON state. The pullup through RCO of the PIOA pin charges the PIOA/PIOB connections to logic `1' level at all devices except for the first device in the chain. If a local VDD supply is not available, the master needs to activate a low-impedance bypass to the 1-Wire pullup resistor immediately after the inverted chain control byte until the PIOA/PIOB connections have reached a voltage equivalent to the logic `1' level. First Cycle: The master sends a Conditional Read ROM command, which causes the first device in the chain to respond with its 64-bit Registration Number. The master memorizes the Registration Number and the fact that this is the first device in the chain. Next the master transmits a Chain DONE command. Through the PIOA pin of the just discovered device, this asserts logic 0 at the PIOB pin of the second device in the chain and also prevents the just discovered device from responding again. Second Cycle: The master sends a Conditional Read ROM command. Since DS28EA00 #2 is the only device in the chain with a LOW level at PIOB it responds with its Registration Number. The master stores the registration number with the sequence number of 2. Device #1 cannot respond since it is in Chain DONE state. Next the master transmits a Chain DONE command. Additional Cycles: To identify the Registration Numbers of the remaining devices and their physical sequence, the master repeats the steps of Conditional Read ROM, and Chain DONE. If there is no response to Conditional Read ROM, all devices in the chain are identified. Ending Condition At the end of the discovery process all devices in the chain are in the Chain DONE state. The master should end the sequence discovery by issuing a Skip ROM command followed by a Chain OFF command. This puts all the devices into the Chain OFF state, and transfers control of the PIOB and PIOA pins to the PIO Access Read and Write function commands.
Figure 16. DS28EA00 Wired for Sequence Discovery ("Chain Function")
VDD 1-Wire Master PX.Y (Microcontroller)
#1
VDD IO DS28EA00 PIOB PIOA *
#2
VDD IO DS28EA00 PIOB PIOA *
#3
VDD IO DS28EA00 PIOB PIOA
GND
GND
GND
* Capacitance of the cabling between adjacent devices in the chain.
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
COMMAND-SPECIFIC 1-Wire COMMUNICATION PROTOCOL--LEGEND
SYMBOL RST PD SELECT SKIPR CDRR WSP RSP CPSP CTEMP RPM RCLE PIOR PIOW CHAIN CRC 00 loop FF loop AA loop xx loop CONVERSION PROGRAMMING DESCRIPTION 1-Wire Reset Pulse generated by master. 1-Wire Presence Pulse generated by slave. Command and data to satisfy the ROM function protocol. ROM Function Command "Skip ROM". ROM Function Command "Conditional Read ROM". Command "Write Scratchpad". Command "Read Scratchpad". Command "Copy Scratchpad". Command "Convert Temperature". Command "Read Power Mode". Command "Recall EEPROM". Command "PIO Access Read". Command "PIO Access Write". Command "Chain". Transfer of n bytes. Transfer of a CRC byte Transfer of a specific byte value "xx" (hexadecimal notation) Indefinite loop where the master reads 00 bytes. Indefinite loop where the master reads FF bytes. Indefinite loop where the master reads AA bytes. Indefinite loop where the slave transmits the inverted invalid control byte. A temperature conversion takes place; activity on the 1-Wire bus is permitted only with local VDD supply. Data transfer to Backup EEPROM; activity on the 1-Wire bus is permitted only with local VDD supply.
COMMAND-SPECIFIC 1-Wire COMMUNICATION PROTOCOL--COLOR CODES
Master to slave Slave to master Programming Conversion
WRITE SCRATCHPAD
RST PD Select WSP <3 bytes> RST PD
READ SCRATCHPAD
RST PD Select RSP <8 bytes> CRC FF loop
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
COPY SCRATCHPAD (PARASITE POWERED)
RST PD Select CPS Wait tPROGMAX FF loop During the wait, the master should activate a lowimpedance bypass to the 1-Wire pullup resistor.
COPY SCRATCHPAD (LOCAL VDD POWERED)
RST PD Select CPS <00h> FF loop The master reads 00h bytes until the write cycle is completed.
CONVERT TEMPERATURE (PARASITE POWERED)
RST PD Select CTEMP Wait tCONVMAX FF loop During the wait, the master should activate a lowimpedance bypass to the 1-Wire pullup resistor.
CONVERT TEMPERATURE (LOCAL VDD POWERED)
RST PD Select CTEMP <00h> FF loop The master reads 00h bytes until the conversion is completed.
READ POWER MODE (PARASITE POWERED)
RST PD Select RPM <00h>
READ POWER MODE (LOCAL VDD POWERED)
RST PD Select RPM
RECALL EEPROM
RST PD Select RCLE <00h> FF loop The master reads 00h bytes until the recall is completed.
PIO ACCESS READ
RST PD Select PIOR See the Command description for behavior if the device is in Chain ON or Chain DONE state.
Continues until master sends Reset Pulse
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DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
PIO ACCESS WRITE (SUCCESS)
RST PD Select PIOW
Loop until master sends Reset Pulse
PIO ACCESS WRITE (INVALID DATA BYTE)
RST PD Select PIOW FF loop
The PIO Access Write command is ignored by the device while in Chain ON or Chain DONE state.
CHANGE CHAIN STATE (SUCCESS)
RST PD Select CHAIN AA loop
CHANGE CHAIN STATE (TRANSMISSION ERROR)
RST PD Select CHAIN < Byte inverted Previous byte> 00 loop
CHANGE CHAIN STATE (INVALID CONTROL BYTE)
RST PD Select CHAIN xx loop
SEQUENCE DISCOVERY EXAMPLE
RST PD SKIPR CHAIN <5Ah> Wait for chain to charge Put all devices into Chain ON state. Identify the first device and put it into Chain DONE state. Identify the next device and put it into Chain DONE state. Repeat this sequence until no device responds.
RST
PD
CDRR

CHAIN
<96h>
<69h>

RST
PD
CDRR

CHAIN
<96h>
<69h>

RST
PD
CDRR
<8 bytes FFh>
No response, all devices have been discovered.
RST
PD
SKIPR
CHAIN
<3Ch>

Put all devices into Chain OFF state.
For the sequence discovery to function properly, the logic state at PIOB (EN\) must not change during the transmission of the Conditional Read ROM command code, and, if the device responds, must stay at logic 0 until the entire 64-bit Registration Number is transmitted.
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