SN74ALS638A, SN74ALS639A, SN74AS638A, SN74AS639

OCTAL BUS TRANSCEIVERS

SDAS123A – DECEMBER 1983 – REVISED JANUARY 1995

Copyright

1

POST OFFICE BOX 655303

High-Density 20-Pin Packages

B-Bus Outputs Are 3 State

Small-Outline (DW) Packages and

Standard Plastic (N) 300-mil DIPs

DEVICE

A

OUTPUT

B

OUTPUT

LOGIC

SN74ALS638A, SN74AS638A

Open collector

3 state

Inverting

SN74ALS639A, SN74AS639

Open collector

3 state

True

description

These octal bus transceivers are designed for asynchronous two-way communication between open-collector

and 3-state buses. The devices transmit data from the A bus (open-collector) to the B bus (3 state) or from the

B bus to the A bus, depending on the logic level at the direction-control (DIR) input. The output-enable (OE) input

can be used to disable the device so the buses are isolated.

The -1 version of SN74ALS638A is identical to the standard version, except that the recommended maximum

The SN74ALS638A, SN74ALS639A, SN74AS638A, and SN74AS639 are characterized for operation from 0

°C

to 70

°C.

FUNCTION TABLE

INPUTS

OPERATION

OE

DIR

SN74ALS638A

SN74AS638A

SN74ALS639A

SN74AS639

L

L

B data to A bus

B data to A bus

L

HA data to B bus

A data to B bus

H

X

Isolation

Isolation

1

2

3

4

5

6

7

8

9

10

20

19

18

17

16

15

14

13

12

11

DIR

A1

A2

A3

A4

A5

A6

A7

A8

GND

OE

B1

B2

B3

B4

B5

B6

B7

B8

DW OR N PACKAGE

(TOP VIEW)

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.