Datasheet

AD670
REV. A
–7–
Table III. AD670 TIMING SPECIFICATIONS
@ +258C
Symbol Parameter Min Typ Max Units
WRITE/CONVERT START MODE
t
W
Write/Start Pulse Width 300 ns
t
DS
Input Data Setup Time 200 ns
t
DH
Input Data Hold 10 ns
t
RWC
Read/Write Setup Before Control 0 ns
t
DC
Delay to Convert Start 700 ns
t
C
Conversion Time 10 µs
READ MODE
t
R
Read Time 250 ns
t
SD
Delay from Status Low to Data Read 250 ns
t
TD
Bus Access Time 200 250 ns
t
DH
Data Hold Time 25 ns
t
DT
Output Float Delay 150 ns
t
RT
R/W before CE or CS low 0 ns
Boldface indicates parameters tested 100% unless otherwise noted. See Specifications page for explanation.
6b. Bipolar
6c. Full Scale (Unipolar)
Figure 6. Transfer Curves
CONTROL AND TIMING OF THE AD670
Control Logic
The AD670 contains on-chip logic to provide conversion and
data read operations from signals commonly available in micro-
processor systems. Figure 7 shows the internal logic circuitry of
the AD670. The control signals,
CE, CS, and R/W control the
operation of the converter. The read or write function is deter-
mined by R/
W when both CS and CE are low as shown in
Table II. If all three control inputs are held low longer than the
conversion time, the device will continuously convert until one
input,
CE, CS, or R/W is brought high. The relative timing of
these signals is discussed later in this section.
Figure 7. Control Logic Block Diagram
Table II. AD670 Control Signal Truth Table
R/W CS CE OPERATION
0 0 0 WRITE/CONVERT
1 0 0 READ
X X 1 NONE
X 1 X NONE
Timing
The AD670 is easily interfaced to a variety of microprocessors
and other digital systems. The following discussion of the timing
requirements of the AD670 control signals will provide the de-
signer with useful insight into the operation of the device.
Write/Convert Start Cycle
Figure 8 shows a complete timing diagram for the write/convert
start cycle.
CS (chip select) and CE (chip enable) are active low
and are interchangeable signals. Both
CS and CE must be low
for the converter to read or start a conversion. The minimum
pulse width, t
W
, on either CS or CE is 300 ns to start a
conversion.