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a
FEATURES Complete 10-Bit A/D Converter with Reference, Clock and Comparator Full 8- or 16-Bit Microprocessor Bus Interface Fast Successive Approximation Conversion--20 s typ No Missing Codes Over Temperature Operates on +5 V and -12 V to -15 V Supplies Low Cost Monolithic Construction
V+
5k
10-Bit A/D Converter AD573*
FUNCTIONAL BLOCK DIAGRAM
V- DIGITAL COMMON CONVERT MSB DB9 DB8
10-BIT CURRENT OUTPUT DAC COMPARATOR 10-BIT SAR
ANALOG IN ANALOG COMMON
DB7 DB6 DB5 HIGH BYTE
BIPOLAR OFFSET CONTROL
INT CLOCK
DB4 DB3 DB2 DB1 DB0 LSB HBE
LOW BYTE
BURIED ZENER REF DATA READY
LBE
AD573
PRODUCT DESCRIPTION
The AD573 is a complete 10-bit successive approximation analog-to-digital converter consisting of a DAC, voltage reference, clock, comparator, successive approximation register (SAR) and three state output buffers--all fabricated on a single chip. No external components are required to perform a full accuracy 10-bit conversion in 20 s. The AD573 incorporates advanced integrated circuit design and processing technologies. The successive approximation function is implemented with I2L (integrated injection logic). Laser trimming of the high stability SiCr thin-film resistor ladder network insures high accuracy, which is maintained with a temperature compensated subsurface Zener reference. Operating on supplies of +5 V and -12 V to -15 V, the AD573 will accept analog inputs of 0 V to +10 V or -5 V to +5 V. The trailing edge of a positive pulse on the CONVERT line initiates the 20 s conversion cycle. DATA READY indicates completion of the conversion. HIGH BYTE ENABLE (HBE) and LOW BYTE ENABLE (LBE) control the 8-bit and 2-bit three state output buffers. The AD573 is available in two versions for the 0C to +70C temperature range, the AD573J and AD573K. The AD573S guarantees 1 LSB relative accuracy and no missing codes from -55C to +125C. Three package configurations are offered. All versions are offered in a 20-pin hermetically sealed ceramic DIP. The AD573J and AD573K are also available in a 20-pin plastic DIP or 20-pin leaded chip carrier.
*Protected by U.S. Patent Nos. 3,940,760; 4,213,806; 4,136,349; 4,400,689; and 4,400,690.
PRODUCT HIGHLIGHTS
l. The AD573 is a complete 10-bit A/D converter. No external components are required to perform a conversion. 2. The AD573 interfaces to many popular microprocessors without external buffers or peripheral interface adapters. The 10 bits of output data can be read as a 10-bit word or as 8and 2-bit words. 3. The device offers true 10-bit accuracy and exhibits no missing codes over its entire operating temperature range. 4. The AD573 adapts to either unipolar (0 V to +10 V) or bipolar (-5 V to +5 V) analog inputs by simply grounding or opening a single pin. 5. Performance is guaranteed with +5 V and -12 V or -15 V supplies. 6. The AD573 is available in a version compliant with MIL-STD883. Refer to the Analog Devices Military Products Databook or current /883B data sheet for detailed specifications.
REV. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
T= = +5 V- = -12 V or -15 AD573-SPECIFICATIONS (@digital+25 C, V+ unlessV,otherwise noted.) V, all voltages measured with respect to common,
A
Model RESOLUTION RELATIVE ACCURACY1 TA = TMIN to TMAX FULL-SCALE CALIBRATION2 UNIPOLAR OFFSET BIPOLAR OFFSET DIFFERENTIAL NONLINEARITY3 TA = TMIN to TMAX TEMPERATURE RANGE TEMPERATURE COEFFICIENTS4 Unipolar Offset Bipolar Offset Full-Scale Calibration2 POWER SUPPLY REJECTION Positive Supply +4.5 V V + +5.5 V Negative Supply -15.75 V V - -14.25 V -12.6 V V - -11.4 V ANALOG INPUT IMPEDANCE ANALOG INPUT RANGES Unipolar Bipolar OUTPUT CODING Unipolar Bipolar LOGIC OUTPUT Output Sink Current (VOUT = 0.4 V max, TMIN to TMAX) Output Source Current5 (VOUT = 2.4 V min, TMIN to TMAX) Output Leakage LOGIC INPUTS Input Current Logic "1" Logic "0" CONVERSION TIME TA = TMIN to TMAX POWER SUPPLY V+ V- OPERATING CURRENT V+ V-
Min
AD573J Typ 10
Max 1 1
Min
AD573K Typ 10
Max 1/2 1/2
Min
AD573S Typ 10
Max 1 1 2 1 1
Units Bits LSB LSB LSB LSB LSB Bits Bits
2 1 1 10 9 0 +70 2 2 4 10 10 0
2 1/2 1/2 10 10 +70 1 1 2 -55
+125 2 2 5
C LSB LSB LSB
2 2 2 3.0 0 -5 5.0 7.0 +10 +5 3.0 0 -5 5.0
1 1 1 7.0 +10 +5 3.0 0 -5 5.0
2 2 2 7.0 +10 +5
LSB LSB LSB k V V
Positive True Binary Positive True Offset Binary
Positive True Binary Positive True Offset Binary
Positive True Binary Positive True Offset Binary
3.2 0.5 40 100 2.0 0.8 10 +4.5 -11.4 20 5.0 -15 15 9 30 +7.0 -16.5 20 15
3.2 0.5 40 100 2.0 0.8 10 +4.5 +11.4 20 +5.0 -15 15 9 30 +7.0 -16.5 20 15
3.2 0.5 40 100 2.0 0.8 10 +4.5 -11.4 20 +5.0 -15 15 9 30 +7.0 -16.5 20 15
mA mA A A V V s V V mA mA
NOTES 1 Relative accuracy is defined as the deviation of the code transition points from the ideal transfer point on a straight line from the zero to the full scale of the device. 2 Full-scale calibration is guaranteed trimmable to zero with an external 50 potentiometer in place of the 15 fixed resistor. Full scale is defined as 10 volts minus 1 LSB, or 9.990 volts. 3 Defined as the resolution for which no missing codes will occur. 4 Change from +25C value from +25C to TMIN or TMAX. 5 The data output lines have active pull-ups to source 0.5 mA. The DATA READY line is open collector with a nominal 6 k internal pull-up resistor. Specifications subject to change without notice. Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. All min and max specifications are guaranteed, although only those shown in boldface are tested on all production units.
-2-
REV. A
AD573
ABSOLUTE MAXIMUM RATINGS
V+ to Digital Common . . . . . . . . . . . . . . . . . . . . . 0 V to +7 V V- to Digital Common . . . . . . . . . . . . . . . . . . . 0 V to -16.5 V Analog Common to Digital Common . . . . . . . . . . . . . . . 1 V Analog Input to Analog Common . . . . . . . . . . . . . . . . . 15 V Control Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V to V+ Digital Outputs (High Impedance State) . . . . . . . . . . 0 V to V+ Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 mW
ORDERING GUIDE1
Model AD573JN AD573KN AD573JP AD573KP AD573JD AD573KD AD573 SD
Package Option2 20-Pin Plastic DIP (N-20) 20-Pin Plastic DIP (N-20) 20-Pin Leaded Chip Carrier (P-20A) 20-Pin Leaded Chip Carrier (P-20A) 20-Pin Ceramic DIP (D-20) 20-Pin Ceramic DIP (D-20) 20-Pin Ceramic DIP (D-20)
Temperature Range 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -55C to +125C
Relative Accuracy 1 LSB max 1/2 LSB max 1 LSB max 1/2 LSB max 1 LSB max 1/2 LSB max 1 LSB max
NOTES 1 For details on grade and package offerings screened in accordance with MIL-STD-883, refer to Analog Devices Military Products Databook. 2 D = Ceramic DIP; N = Plastic DIP; P = Plastic Leaded Chip Carrier.
FUNCTIONAL DESCRIPTION
A block diagram of the AD573 is shown in Figure 1. The positive CONVERT pulse must be at least 500 ns wide. DR goes high within 1.5 s after the leading edge of the convert pulse indicating that the internal logic has been reset. The negative edge of the CONVERT pulse initiates the conversion. The internal 10-bit current output DAC is sequenced by the integrated injection logic (I2L) successive approximation register (SAR) from its most significant bit to least significant bit to provide an output current which accurately balances the input signal current through the 5 k resistor. The comparator determines whether the addition of each successively weighted bit current causes the DAC current sum to be greater or less than the input current; if the sum is more, the bit is turned off. After testing all bits, the SAR contains a 10-bit binary code which accurately represents the input signal to within 1/2 LSB (0.05% of full scale). The SAR drives DR low to indicate that the conversion is complete and that the data is available to the output buffers. HBE and LBE can then be activated to enable the upper 8-bit and lower 2-bit buffers as desired. HBE and LBE should be brought high prior to the next conversion to place the output buffers in the high impedance state. The temperature compensated buried Zener reference provides the primary voltage reference to the DAC and ensures excellent stability with both time and temperature. The bipolar offset input controls a switch which allows the positive bipolar offset current (exactly equal to the value of the MSB less 1/2 LSB) to be injected into the summing (+) node of the comparator to offset the DAC output. Thus the nominal 0 V to +10 V unipolar input range becomes a -5 V to +5 V range. The 5 k thin-film input resistor is trimmed so that with a full-scale input signal, an input current will be generated which exactly matches the DAC output with all bits on.
V+
5k
V-
DIGITAL COMMON
CONVERT MSB DB9 DB8
ANALOG IN ANALOG COMMON
10-BIT CURRENT OUTPUT DAC COMPARATOR
10-BIT SAR
DB7 DB6 DB5 HIGH BYTE
BIPOLAR OFFSET CONTROL
INT CLOCK
DB4 DB3 DB2 DB1 DB0 LSB HBE
LOW BYTE
BURIED ZENER REF DATA READY
LBE
AD573
Figure 1. Functional Block Diagram
UNIPOLAR CONNECTION
The AD573 contains all the active components required to perform a complete A/D conversion. Thus, for many applications, all that is necessary is connection of the power supplies (+5 V and -12 V to -15 V), the analog input and the convert pulse. However, there are some features and special connections which should be considered for achieving optimum performance. The functional pinout is shown in Figure 2. The standard unipolar 0 V to +10 V range is obtained by shorting the bipolar offset control pin (Pin 16) to digital common (Pin 17).
REV. A
-3-
AD573
LSB DB0 1 DB1 2 DB2 3 DB3 4 DB4 5 DB5 6
PIN 1 IDENTIFIER
20 HBE 19 LBE 18 DR 17 DIG COM
Figure 4a shows how the converter zero may be offset by up to 3 bits to correct the device initial offset and/or input signal offsets. As shown, the circuit gives approximately symmetrical adjustment in unipolar mode.
AD573
16 BIP OFF
TOP VIEW 15 ANALOG COM (Not to Scale) DB6 7 14 ANALOG IN DB7 8 DB8 9 MSB DB9 10 13 V- 12 CONVERT 11 V+
Figure 2. AD573 Pin Connections
Full-Scale Calibration
The 5 k thin-film input resistor is laser trimmed to produce a current which matches the full-scale current of the internal DAC--plus about 0.3%--when an analog input voltage of 9.990 volts (10 volts - 1 LSB) is applied at the input. The input resistor is trimmed in this way so that if a fine trimming potentiometer is inserted in series with the input signal, the input current at the full-scale input voltage can be trimmed down to match the DAC full-scale current as precisely as desired. However, for many applications the nominal 9.99 volt full scale can be achieved to sufficient accuracy by simply inserting a 15 resistor in series with the analog input to Pin 14. Typical full-scale calibration error will then be within 2 LSB or 0.2%. If more precise calibration is desired, a 50 trimmer should be used instead. Set the analog input at 9.990 volts, and set the trimmer so that the output code is just at the transition between 11111111 10 and 11111111 11. Each LSB will then have a weight of 9.766 mV. If a nominal full scale of 10.24 volts is desired (which makes the LSB have a weight of exactly 10.00 mV), a 100 resistor and a 100 trimmer (or a 200 trimmer with good resolution) should be used. Of course, larger full-scale ranges can be arranged by using a larger input resistor, but linearity and full-scale temperature coefficient may be compromised if the external resistor becomes a sizeable percentage of 5 k. Figure 3 illustrates the connections required for full-scale calibration.
Figure 4a. Figure 4b. Figure 4. Offset Trims
Figure 5 shows the nominal transfer curve near zero for an AD573 in unipolar mode. The code transitions are at the edges of the nominal bit weights. In some applications it will be preferable to offset the code transitions so that they fall between the nominal bit weights, as shown in the offset characteristics.
Figure 5. AD573 Transfer Curve--Unipolar Operation (Approximate Bit Weights Shown for Illustration, Nominal Bit Weights ~ 9.766 mV)
This offset can easily be accomplished as shown in Figure 4b. At balance (after a conversion) approximately 2 mA flows into the Analog Common terminal. A 2.7 resistor in series with this terminal will result in approximately the desired 1/2 bit offset of the transfer characteristics. The nominal 2 mA Analog Common current is not closely controlled in manufacture. If high accuracy is required, a 5 potentiometer (connected as a rheostat) can be used as R1. Additional negative offset range may be obtained by using larger values of R1. Of course, if the zero transition point is changed, the full-scale transition point will also move. Thus, if an offset of 1/2 LSB is introduced, full-scale trimming as described on the previous page should be done with an analog input of 9.985 volts. NOTE: During a conversion, transient currents from the Analog Common terminal will disturb the offset voltage. Capacitive decoupling should not be used around the offset network. These transients will settle appropriately during a conversion. Capacitive decoupling will "pump up" and fail to settle resulting in conversion errors. Power supply decoupling, which returns to analog signal common, should go to the signal input side of the resistive offset network.
Figure 3. Standard AD573 Connections
Unipolar Offset Calibration
Since the Unipolar Offset is less than 1 LSB for all versions of the AD573, most applications will not require trimming. Figure 4 illustrates two trimming methods which can be used if greater accuracy is necessary. -4-
REV. A
AD573
BIPOLAR CONNECTION
To obtain the bipolar -5 V to +5 V range with an offset binary output code, the bipolar offset control pin is left open. A -5.000 volt signal will give a 10-bit code of 00000000 00; an input of 0.000 volts results in an output code of 10000000 00 and +4.99 volts at the input yields the 11111111 11 code. The nominal transfer curve is shown in Figure 6.
SAMPLE-HOLD AMPLIFIER CONNECTION TO THE AD573
Many situations in high speed acquisition systems or digitizing rapidly changing signals require a sample-hold amplifier (SHA) in front of the A/D converter. The SHA can acquire and hold a signal faster than the converter can perform a conversion. A SHA can also be used to accurately define the exact point in time at which the signal is sampled. For the AD573, a SHA can also serve as a high input impedance buffer. Figure 8 shows the AD573 connected to the AD582 monolithic SHA for high speed signal acquisition. In this configuration, the AD582 will acquire a 10 volt signal in less than 10 s with a droop rate less than 100 V/ms.
Figure 6. AD573 Transfer Curve-- Bipolar Operation
Note that in the bipolar mode, the code transitions are offset 1/2 LSB such that an input voltage of 0 volts 5 mV yields the code representing zero (10000000 00). Each output code is then centered on its nominal input voltage.
Full-Scale Calibration
Full-Scale Calibration is accomplished in the same manner as in unipolar operation except the full scale input voltage is +4.985 volts.
Negative Full-Scale Calibration
The circuit in Figure 4a can also be used in bipolar operation to offset the input voltage (nominally -5 V) which results in the 00000000 00 code. R2 should be omitted to obtain a symmetrical range. The bipolar offset control input is not directly TTL compatible but a TTL interface for logic control can be constructed as shown in Figure 7.
Figure 8. Sample-Hold Interface to the AD573
DR goes high after the conversion is initiated to indicate that reset of the SAR is complete. In Figure 8 it is also used to put the AD582 into the hold mode while the AD573 begins its conversion cycle. (The AD582 settles to final value well in advance of the first comparator decision inside the AD573). DR goes low when the conversion is complete placing the AD582 back in the sample mode. Configured as shown in Figure 8, the next conversion can be initiated after a 10 s delay to allow for signal acquisition by the AD582. Observe carefully the ground, supply, and bypass capacitor connections between the two devices. This will minimize ground noise and interference during the conversion cycle.
GROUNDING CONSIDERATIONS
The AD573 provides separate Analog and Digital Common connections. The circuit will operate properly with as much as 200 mV of common-mode voltage between the two commons. This permits more flexible control of system common bussing and digital and analog returns.
Figure 7. Bipolar Offset Controlled by Logic Gate Gate Output = 1 Unipolar 0-10 V Input Range Gate Output = 0 Bipolar 5 V Input Range
In normal operation, the Analog Common terminal may generate transient currents of up to 2 mA during a conversion. In addition a static current of about 2 mA will flow into Analog Common in the unipolar mode after a conversion is complete. The Analog Common current will be modulated by the variations in input signal. The absolute maximum voltage rating between the two commons is 1 volt. It is recommended that a parallel pair of back-to-back protection diodes be connected between the commons if they are not connected locally.
REV. A
-5-
AD573
CONTROL AND TIMING OF THE AD573
The operation of the AD573 is controlled by three inputs: CONVERT, HBE and LBE.
Starting a Conversion
The conversion cycle is initiated by a positive going CONVERT pulse at least 500 ns wide. The rising edge of this pulse resets the internal logic, clears the result of the previous conversion, and sets DR high. The falling edge of CONVERT begins the conversion cycle. When conversion is completed DR returns low. During the conversion cycle, HBE and LBE should be held high. If HBE or LBE goes low during a conversion, the data output buffers will be enabled and intermediate conversion results will be present on the data output pins. This may cause bus conflicts if other devices in a system are trying to use the bus.
VIH + VIL 2 CONVERT
pulse, and gating it with RD to enable the output buffers. The use of a memory address and memory WR and RD signals denotes "memory-mapped" I/O interfacing, while the use of a separate I/O address space denotes "isolated I/O" interfacing. In 8-bit bus systems, the 10-bit AD573 will occupy two locations when data is to be read; therefore, two (usually consecutive) addresses must be decoded. One of the addresses can also be used as the address which produces the CONVERT signal during WR operations. Figure 11 shows a generalized diagram of the control logic for an AD573 interfaced to an 8-bit data bus, where two addresses (ADC ADDR and ADC ADDR + 1) have been decoded. ADC ADDR starts the converter when written to (the actual data being written to the converter does not matter) and contains the high byte data during read operations. ADC ADDR + 1 performs no function during write operations, but contains the low byte data during read operations.
tC tCS tDSC
DR
VOH + VOL 2
Figure 9. Convert Timing
Reading the Data
The three-state data output buffers are enabled by HBE and LBE. Access time of these buffers is typically 150 ns (250 maximum). The data outputs remain valid until 50 ns after the enable signal returns high, and are completely into the high impedance state 100 ns later.
LBE OR HBE VIH + VIL 2 HIGH IMPEDANCE
tDD
VOH VOL DATA VALID
tHD
Figure 11. General AD573 Interface to 8-Bit Microprocessor
HIGH IMPEDANCE
DB0-DB7 OR DB8-DB9
tHL
Figure 10. Read Timing
TIMING SPECIFICATIONS (All grades, TA = TMIN-TMAX)
Parameter CONVERT Pulse Width DR Delay from CONVERT Conversion Time Data Access Time Data Valid after HBE/LBE High Output Float Delay
Symbol Min Typ Max Units tCS tDSC tC tDD tHD tHL 500 - 10 0 50 - - 1 20 150 - 100 - 1.5 30 250 - 200 ns s s ns ns ns
In systems where this read-write interface is used, at least 30 microseconds (the maximum conversion time) must be allowed to pass between starting a conversion and reading the results. This delay or "timeout" period can be implemented in a short software routine such as a countdown loop, enough dummy instructions to consume 30 microseconds, or enough actual useful instructions to consume the required time. In tightly-timed systems, the DR line may be read through an external three-state buffer to determine precisely when a conversion is complete. Higher speed systems may choose to use DR to signal an interrupt to the processor at the end of a conversion.
MICROPROCESSOR INTERFACE CONSIDERATIONS-- GENERAL
When an analog-to-digital converter like the AD573 is interfaced to a microprocessor, several details of the interface must be considered. First, a signal to start the converter must be generated; then an appropriate delay period must be allowed to pass before valid conversion data may be read. In most applications, the AD573 can interface to a microprocessor system with little or no external logic. The most popular control signal configuration consists of decoding the address assigned to the AD573, then gating this signal with the system's WR signal to generate the CONVERT -6-
Figure 12. Typical AD573 Interface Timing Diagram
REV. A
AD573
CONVERT Pulse Generation
The AD573 is tested with a CONVERT pulse width of 500 ns and will typically operate with a pulse as short as 300 ns. However, some microprocessors produce active WR pulses which are shorter than this. Either of the circuits shown in Figure 13 can be used to generate an adequate CONVERT pulse for the AD573. In both circuits, the short low going WR pulse sets the CONVERT line high through a flip-flop. The rising edge of DR (which signifies that the internal logic has been reset) resets the flip-flop and brings CONVERT low, which starts the conversion. Note that tDSC is slightly longer when the result of the previous conversion contains a Logic 1 on the LSB. This means that the actual CONVERT pulse generated by the circuits in Figure 13 will vary slightly in width.
This mode is particularly useful for bench-testing of the AD573, and in applications where dedicated I/O ports of peripheral interface adapter chips are available.
Figure 15. AD573 in "Stand-Alone" Mode (Output Data Valid 500 ns After DR Goes Low)
Apple II Microcomputer Interface
The AD573 can provide a flexible, low cost analog interface for the popular Apple II microcomputer. The Apple II, based on a 1 MHz 6502 microprocessor, meets all timing requirements for the AD573. Only a few TTL gates are required to decode the signals available on the Apple II's peripheral connector. The recommended connections are shown in Figure 16.
Figure 13a. Using 74LS00
Output Data Format
Figure 13b. Using 1/2 74LS74
The AD573 output data is presented in a left justified format. The 8 MSBs (DB9-DB2, Pins 10 through 3) are enabled by HBE (Pin 20) and the 2 LSBs (DB1, DB0--Pins 2 and 1) are enabled by LBE (Pin 19). This allows simple interface to 8-bit system buses by overlapping the 2 MSBs and the 2 LSBs. The organization of the data is shown in Figure 14. When the least significant bits are read (LBE brought low), the six remaining bits of the byte will contain meaningless data. These unwanted bits can be masked by logically ANDing the byte with 11000000 (C0 hex), which forces the 6 lower bits to Logic 0 while preserving the two most significant bits of the byte. Note that it is not possible to reconfigure the AD573 for right justified data.
Figure 16. AD573 Interface to Apple ll Figure 14. AD573 Output Data Format
In systems where all 10 bits are desired at the same time, HBE and LBE may be tied together. This is useful in interfacing to 16-bit bus systems. The resulting 10-bit word can then be placed at the high end of the 16-bit bus for left justification or at the low end for right justification. It is also possible to use the AD573 in a "stand-alone" mode, where the output data buffers are automatically enabled at the end of a conversion cycle. In this mode, the DR output is wired to the HBE and LBE inputs. The outputs thus are forced into the high impedance state during the conversion period, and valid data becomes available approximately 500 ns after the DR signal goes low at the end of the conversion. The 500 ns delay allows propagation of the least significant bit through the internal logic. REV. A
The BASIC routine listed here will operate the AD573 circuit shown in Figure 16. The conversion is started by POKEing to the location which contains the AD573. The relatively slow execution speed of BASIC eliminates the need for a delay routine between starting and reading the converter. This routine assumes that the AD573 is connected for a 5 volt input range. Variable I represents the integer value (from 0 to 1023) read from the AD573. Variable V represents the actual value of the input signal (in volts). 100 110 120 130 140 150 160 -7- PRINT "WHICH SLOT IS THE A/D IN";:INPUT S A=49280 + 16*S POKE A,0 L=PEEK(A) :H=PEEK(A+1) I =(4*H) + INT(L/64) V=(I/1024)*10-5 PRINT "THE INPUT SIGNAL IS";V;"VOLTS."
AD573
It is also possible to write a faster-executing assembly-language routine to control the AD573. Such a routine will require a delay between starting and reading the converter. This can be easily implemented by calling the Apple's WAIT subroutine (which resides at location $FCA8) after loading the accumulator with a number greater than or equal to two.
8085-Series Microprocessor Interface OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
20-Pin Ceramic DIP Package ("D")
The AD573 can also be used with 8085-series microprocessors. These processors use separate control signals for RD and WR, as opposed to the single R/W control signal used in the 6800/ 6500 series processors. There are two constraints related to operation of the AD573 with 8085-series processors. The first problem is the width of the CONVERT pulse. The circuit shown in Figure 17 (essentially the same as that shown in Figure 13) will produce a wide enough CONVERT pulse when the 8085 is running at 5 MHz. For 8085 systems running at slower clock rates (3 MHz), the flip-flop-based circuit can be eliminated since the WR pulse will be approximately 500 ns wide. The other consideration is the access time of the AD573's threestate output data buffers, which is 250 ns maximum. It may be necessary to insert wait states during RD operations from the AD573. This will not be a problem in systems using memories with comparable access times, since wait states will have already been provided in the basic system design.
20-Pin Plastic DIP Package ("N")
P-20A PLCC
Figure 17. AD573-8085A Interface Connections
ADC: LXI H, 3000 MOV M, A MVI B, 06 LOOP: DCR B JNZ LOOP MOV A, M ANI C0 MOV E, A INR L MOV D, M RET
; LOAD HL WITH AD573 ADDRESS ; START CONVERSION ; LOAD DELAY PERIOD ; DELAY LOOP ; ; READ LOW BYTE ; MASK LOWER 6 BITS ; STORE CLEAN LOW BYTE IN E ; LOAD HIGH BYTE ADDRESS ; MOVE HIGH BYTE TO D ; EXIT
-8-
REV. A
PRINTED IN U.S.A.
The following assembly-language subroutine can be used to control an AD573 residing at memory locations 3000H and 3001H. The 10 bits of data are returned (left-justified) in the DE register pair.
C841-9-5/84
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