AD670
6b. Bipolar
Figure 7. Control Logic Block Diagram
Table II. AD670 Control Signal Truth Table
R/W
CS
CE
OPERATION
0
1
0
0
0
0
WRITE/CONVERT
READ
X
X
X
1
1
X
NONE
NONE
6c. Full Scale (Unipolar)
Figure 6. Transfer Curves
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.
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.
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, tW, on either CS or CE is 300 ns to start a
conversion.
Table III. AD670 TIMING SPECIFICATIONS
@ +25؇C
Symbol
Parameter
Min
Typ
Max
Units
WRITE/CONVERT START MODE
tW
Write/Start Pulse Width
Input Data Setup Time
Input Data Hold
Read/Write Setup Before Control
Delay to Convert Start
Conversion Time
300
200
10
ns
ns
ns
ns
ns
µs
tDS
tDH
tRWC
tDC
tC
0
700
10
READ MODE
tR
Read Time
Delay from Status Low to Data Read
Bus Access Time
Data Hold Time
Output Float Delay
250
ns
ns
ns
ns
ns
ns
tSD
tTD
tDH
tDT
tRT
250
250
200
25
0
150
R/W before CE or CS low
Boldface indicates parameters tested 100% unless otherwise noted. See Specifications page for explanation.
REV. A
–7–
ADI [ ADI ]
