CONTROLLING THE ADS774H

ADS774H

reading the output data when ready: choosing either

12 bits all at once, or the eight MSBs followed by the

The

ADS774H

can

easily

interface

with

most

four LSBs in a left-justified format. The five control

microprocessors and other digital systems. The

inputs

(12/8,

CS,

microprocessor

may

take

full

control

of

each

TTL-/CMOS-compatible. The functions of the control

conversion, or the converter may operate in a

inputs are described in Table 1. The control function

stand-alone mode, controlled only by the R/C input.

truth table is shown in Table 2.

Full control consists of selecting an 8- or 12-bit

conversion

cycle,

initiating

the

conversion,

and

Table 1. Control Line Functions

DESIGNATION

DEFINITION

FUNCTION

Must be high ('1') to either initiate a conversion or read output data. 0-to-1 edge

CE (pin 6)

Chip Enable (active high)

may be used to initiate a conversion.

Must be low ('0') to either initiate a conversion or read output data. 1-to-0 edge

CS (pin 3)

Chip Select (active low)

may be used to initiate a conversion.

Must be low ('0') to initiate either 8- or 12-bit conversions. 1-to-0 edge may be used

Read/Convert

to initiate a conversion.

R/C (pin 5)

'1' = Read

Must be high ('1') to read output data. 0-to-1 edge may be used to initiate a read

'0' = Convert

operation.

Byte Address, short cycle

Data Mode select

When reading output data, 12/8 = '1' enables all 12 output bits simultaneously.

12/8 (pin 2)

'1' = 12-bit

'0' = 8-bit

Table 2. Control Input Truth Table

CE

CS

R/C

12/8

OPERATION

0

X

X

X

X

None

X

1

X

X

X

None

↑

0

0

X

0

Initiate 12-bit conversion

↑

0

0

X

1

Initiate 8-bit conversion

1

↓

0

X

0

Initiate 12-bit conversion

1

↓

0

X

1

Initiate 8-bit conversion

1

0

↓

X

0

Initiate 12-bit conversion

1

0

↓

X

1

Initiate 8-bit conversion

1

0

1

1

X

Enable 12-bit output

1

0

1

0

0

Enable eight MSBs only

Enable four LSBs plus four trailing

1

0

1

0

1

zeroes

Copyright © 2009, Texas Instruments Incorporated

Submit Documentation Feedback

13