FUNCTIONAL BLOCK DIAGRAM
BURIED ZENER REF
COMP-
ARATOR
ANALOG
IN
DB9
HIGH
BYTE
10-BIT
CURRENT
OUTPUT
DAC
V+
V
DIGITAL
COMMON
CONVERT
INT
CLOCK
10-BIT
SAR
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
HBE
LBE
MSB
LSB
LOW
BYTE
ANALOG
COMMON
BIPOLAR
OFFSET
CONTROL
DATA
READY
AD573
5k
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.
a
10-Bit A/D Converter
AD573*
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
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
PRODUCT DESCRIPTION
The AD573 is a complete 10-bit successive approximation
analog-to-digital converter consisting of a DAC, voltage refer-
ence, 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 I
2
L (integrated injection logic). Laser trim-
ming 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 0
C to +70
C
temperature range, the AD573J and AD573K. The AD573S
guarantees
1 LSB relative accuracy and no missing codes from
55
C to +125
C.
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 8-
and 2-bit words.
3. The device offers true 10-bit accuracy and exhibits no miss-
ing 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-STD-
883. Refer to the Analog Devices Military Products Data-
book or current /883B data sheet for detailed specifications.
AD573SPECIFICATIONS
(@ T
A
= +25 C, V+ = +5 V, V = 12 V or 15 V, all voltages measured with respect
to digital common, unless otherwise noted.)
AD573J
AD573K
AD573S
Model
Min
Typ
Max
Min
Typ
Max
Min
Typ
Max
Units
RESOLUTION
10
10
10
Bits
RELATIVE ACCURACY
1
1
1/2
1
LSB
T
A
= T
MIN
to T
MAX
1
1/2
1
LSB
FULL-SCALE CALIBRATION
2
2
2
2
LSB
UNIPOLAR OFFSET
1
1/2
1
LSB
BIPOLAR OFFSET
1
1/2
1
LSB
DIFFERENTIAL NONLINEARITY
3
10
10
10
Bits
T
A
= T
MIN
to T
MAX
9
10
10
Bits
TEMPERATURE RANGE
0
+70
0
+70
55
+125
C
TEMPERATURE COEFFICIENTS
4
Unipolar Offset
2
1
2
LSB
Bipolar Offset
2
1
2
LSB
Full-Scale Calibration
2
4
2
5
LSB
POWER SUPPLY REJECTION
Positive Supply
+4.5 V
V +
+5.5 V
2
1
2
LSB
Negative Supply
15.75 V
V
14.25 V
2
1
2
LSB
12.6 V
V
11.4 V
2
1
2
LSB
ANALOG INPUT IMPEDANCE
3.0
5.0
7.0
3.0
5.0
7.0
3.0
5.0
7.0
k
ANALOG INPUT RANGES
Unipolar
0
+10
0
+10
0
+10
V
Bipolar
5
+5
5
+5
5
+5
V
OUTPUT CODING
Unipolar
Positive True Binary
Positive True Binary
Positive True Binary
Bipolar
Positive True Offset Binary
Positive True Offset Binary
Positive True Offset Binary
LOGIC OUTPUT
Output Sink Current
(V
OUT
= 0.4 V max, T
MIN
to T
MAX
)
3.2
3.2
3.2
mA
Output Source Current
5
(V
OUT
= 2.4 V min, T
MIN
to T
MAX
)
0.5
0.5
0.5
mA
Output Leakage
40
40
40
A
LOGIC INPUTS
Input Current
100
100
100
A
Logic "1"
2.0
2.0
2.0
V
Logic "0"
0.8
0.8
0.8
V
CONVERSION TIME
T
A
= T
MIN
to T
MAX
10
20
30
10
20
30
10
20
30
s
POWER SUPPLY
V+
+4.5
5.0
+7.0
+4.5
+5.0
+7.0
+4.5
+5.0
+7.0
V
V
11.4
15
16.5
+11.4
15
16.5
11.4
15
16.5
V
OPERATING CURRENT
V+
15
20
15
20
15
20
mA
V
9
15
9
15
9
15
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 +25
C value from +25
C to T
MIN
or T
MAX
.
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.
REV. A
2
AD573
REV. A
3
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 GUIDE
1
Temperature
Relative
Model
Package Option
2
Range
Accuracy
AD573JN
20-Pin Plastic DIP (N-20)
0
C to +70
C
1 LSB max
AD573KN
20-Pin Plastic DIP (N-20)
0
C to +70
C
1/2 LSB max
AD573JP
20-Pin Leaded Chip Carrier (P-20A)
0
C to +70
C
1 LSB max
AD573KP
20-Pin Leaded Chip Carrier (P-20A)
0
C to +70
C
1/2 LSB max
AD573JD
20-Pin Ceramic DIP (D-20)
0
C to +70
C
1 LSB max
AD573KD
20-Pin Ceramic DIP (D-20)
0
C to +70
C
1/2 LSB max
AD573 SD
20-Pin Ceramic DIP (D-20)
55
C to +125
C
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 posi-
tive 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 in-
ternal 10-bit current output DAC is sequenced by the integrated
injection logic (I
2
L) successive approximation register (SAR)
from its most significant bit to least significant bit to provide an
output current which accurately balances the input signal cur-
rent 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 com-
plete 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 in-
put 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.
BURIED ZENER REF
COMP-
ARATOR
ANALOG
IN
DB9
HIGH
BYTE
10-BIT
CURRENT
OUTPUT
DAC
V+
V
DIGITAL
COMMON
CONVERT
INT
CLOCK
10-BIT
SAR
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
HBE
LBE
MSB
LSB
LOW
BYTE
ANALOG
COMMON
BIPOLAR
OFFSET
CONTROL
DATA
READY
AD573
5k
Figure 1. Functional Block Diagram
UNIPOLAR CONNECTION
The AD573 contains all the active components required to per-
form 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 short-
ing the bipolar offset control pin (Pin 16) to digital common
(Pin 17).
AD573
REV. A
4
14
13
12
11
17
16
15
20
19
18
10
9
8
1
2
3
4
7
6
5
TOP VIEW
(Not to Scale)
AD573
LSB DB0
DIG COM
DR
LBE
HBE
DB1
DB2
DB3
ANALOG IN
ANALOG COM
BIP OFF
DB4
DB5
DB6
DB7
DB8
MSB DB9
V+
CONVERT
V
PIN 1
IDENTIFIER
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 resis-
tor is trimmed in this way so that if a fine trimming potentiom-
eter 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
resis-
tor 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 de-
sired (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 lin-
earity and full-scale temperature coefficient may be compro-
mised if the external resistor becomes a sizeable percentage of
5 k
. Figure 3 illustrates the connections required for full-scale
calibration.
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.
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.
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 pref-
erable 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 accu-
racy is required, a 5
potentiometer (connected as a rheostat)
can be used as R1. Additional negative offset range may be ob-
tained by using larger values of R1. Of course, if the zero transi-
tion 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. Capaci-
tive 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.
AD573
REV. A
5
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.
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 symmetri-
cal 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 7. Bipolar Offset Controlled by Logic Gate
Gate Output = 1 Unipolar 010 V Input Range
Gate Output = 0 Bipolar
5 V Input Range
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 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 con-
version 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 Fig-
ure 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 con-
nections 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.
In normal operation, the Analog Common terminal may gener-
ate transient currents of up to 2 mA during a conversion. In ad-
dition 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 varia-
tions in input signal.
The absolute maximum voltage rating between the two com-
mons is
1 volt. It is recommended that a parallel pair of
back-to-back protection diodes be connected between the com-
mons if they are not connected locally.
AD573
REV. A
6
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 re-
sults 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.
t
CS
t
DSC
V
OH
+ V
OL
2
V
IH
+ V
IL
2
t
C
CONVERT
DR
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 maxi-
mum). The data outputs remain valid until 50 ns after the en-
able signal returns high, and are completely into the high
impedance state 100 ns later.
V
IH
+ V
IL
2
LBE
OR
HBE
t
HD
t
DD
V
OH
V
OL
DATA
VALID
t
HL
HIGH
IMPEDANCE
HIGH
IMPEDANCE
DB0DB7
OR
DB8DB9
Figure 10. Read Timing
TIMING SPECIFICATIONS (All grades, T
A
= T
MIN
T
MAX
)
Parameter
Symbol Min Typ
Max Units
CONVERT Pulse Width
t
CS
500
ns
DR
Delay from CONVERT t
DSC
1
1.5
s
Conversion Time
t
C
10
20
30
s
Data Access Time
t
DD
0
150
250
ns
Data Valid after HBE/LBE
High
t
HD
50
ns
Output Float Delay
t
HL
100
200
ns
MICROPROCESSOR INTERFACE CONSIDERATIONS--
GENERAL
When an analog-to-digital converter like the AD573 is inter-
faced to a microprocessor, several details of the interface must
be considered. First, a signal to start the converter must be gen-
erated; 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 de-
coding the address assigned to the AD573, then gating this sig-
nal with the system's WR signal to generate the CONVERT
pulse, and gating it with RD to enable the output buffers. The
use of a memory address and memory WR and RD signals de-
notes "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) ad-
dresses 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 be-
ing written to the converter does not matter) and contains the
high byte data during read operations. ADC ADDR + 1 per-
forms no function during write operations, but contains the low
byte data during read operations.
Figure 11. General AD573 Interface to 8-Bit Microprocessor
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 in-
structions to consume 30 microseconds, or enough actual useful
instructions to consume the required time. In tightly-timed sys-
tems, 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 inter-
rupt to the processor at the end of a conversion.
Figure 12. Typical AD573 Interface Timing Diagram
AD573
REV. A
7
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 Fig-
ure 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 t
DSC
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.
Figure 13a. Using 74LS00 Figure 13b. Using 1/2 74LS74
Output Data Format
The AD573 output data is presented in a left justified format.
The 8 MSBs (DB9DB2, 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 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 inter-
nal logic.
This mode is particularly useful for bench-testing of the AD573,
and in applications where dedicated I/O ports of peripheral in-
terface 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 16. AD573 Interface to Apple ll
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 ex-
ecution speed of BASIC eliminates the need for a delay routine
between starting and reading the converter. This routine as-
sumes 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 PRINT "WHICH SLOT IS THE A/D IN";:INPUT S
110 A=49280 + 16*S
120 POKE A,0
130 L=PEEK(A) :H=PEEK(A+1)
140 I =(4*H) + INT(L/64)
150 V=(I/1024)*10-5
160 PRINT "THE INPUT SIGNAL IS";V;"VOLTS."
AD573
REV. A
8
C84195/84
PRINTED IN U.S.A.
It is also possible to write a faster-executing assembly-language
routine to control the AD573. Such a routine will require a de-
lay between starting and reading the converter. This can be eas-
ily 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
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 (essen-
tially 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 three-
state 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.
Figure 17. AD5738085A Interface Connections
The following assembly-language subroutine can be used to
control an AD573 residing at memory locations 3000
H
and
3001
H
. The 10 bits of data are returned (left-justified) in the
DE register pair.
ADC:
LXI H, 3000 ; LOAD HL WITH AD573 ADDRESS
MOV M, A
; START CONVERSION
MVI B, 06
; LOAD DELAY PERIOD
LOOP: DCR B
; DELAY LOOP
JNZ LOOP
;
MOV A, M
; READ LOW BYTE
ANI C0
; MASK LOWER 6 BITS
MOV E, A
; STORE CLEAN LOW BYTE IN E
INR L
; LOAD HIGH BYTE ADDRESS
MOV D, M
; MOVE HIGH BYTE TO D
RET
; EXIT
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
20-Pin Ceramic DIP Package ("D")
20-Pin Plastic DIP Package ("N")
P-20A PLCC
PDF 
ZIP