AD670

REV. A

–7–

Table III. AD670 TIMING SPECIFICATIONS

@ +25 C

Symbol

Parameter

Min

Typ

Max

Units

WRITE/CONVERT START MODE

Write/Start Pulse Width

300

ns

Input Data Setup Time

200

ns

Input Data Hold

10

ns

Read/Write Setup Before Control

0

ns

Delay to Convert Start

700

ns

Conversion Time

10

µs

READ MODE

Read Time

250

ns

Delay from Status Low to Data Read

250

ns

Bus Access Time

200

250

ns

Data Hold Time

25

ns

Output Float Delay

150

ns

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

conversion.