4

®

ADC674A

PIN CONFIGURATION

PIN

DESIGNATION

DEFINITION

FUNCTION

CE (Pin 6)

Chip Enable

Must be high (“1”) to either initiate a conversion or read output data. 0-1 edge may be used to initiate a

(active high)

conversion.

CS (Pin 3)

Chip Select

Must be low (“0”) ot either initiate a conversion or read output data. 1-0 edge may be used to initiate a conversion.

(active low)

R/C (Pin 5)

Read/Convert

Must be low (“0”) to initiate either 8- or 12-bit conversions. 1-0 edge may be used to initiate a conversion. Must be high

(“1” = read)

(“1”) to read output data. 0-1 edge may be used to initiate a read operation.

(“0” = convert)

Byte Address

Short Cycle

byte).

12/8 (Pin 2)

Data Mode Select

When reading output data. 12/8 = “1” enables all 12 output bits simultaneously. 12/8 = “0” will enable the MSBs

(“1” = 12-bits)

(“0” = 8-bits)

TABLE I. ADC674A Control Line Functions.

CONTROLLING THE ADC674A

The Burr-Brown ADC674A can be easily interfaced to most

microprocessor systems and other digital systems. The mi-

croprocessor may take full control of each conversion, or the

converter may operate in a stand-alone mode, controlled

only by the R/C input. Full control consists of selecting an

8- or 112-bit conversion cycle, initiating the conversion, and

the output data when ready—choosing either 12 bits all at

once, or 8 bits followed by 4 bits in a left-justified format.

The five control inputs (12/8, CS, A

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

puts are described in Table I. The control function truth table

is listed in Table II.

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

10

↓

X

0

Initiate 12-bit conversion

10

↓

X

1

Initiate 8-bit conversion

1

0

1

1

X

Enable 12-bit output

1

0

1

0

0

Enable 8 MSBs only

1

0

1

0

1

Enable 4 LSBs plus 4

trailing zeros

TABLE II. Control Input Truth Table.

+5VDC Supply (V

)

12/8

CS

A

R/C

CE

+V

Ref Out

Analog Common

Ref In

V

Bipolar Offset

10V Range

20V Range

Status

DB11 (MSB)

DB10

DB9

DB8

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0 (LSB)

Digital Common

1

2

3

4

5

6

7

8

9

10

11

12

13

14

28

27

26

25

24

23

22

21

20

19

18

17

16

15

LOGIC

CC

EE

5k

Ω

10k

Ω

10V

Reference

12-Bit

D/A

Converter

Control

Logic

Power-up Reset

Clock

12 Bits

Comparator

12 Bits

O

5k

Ω