1

Data sheet acquired from Harris Semiconductor

SCHS193A

Features

• Independent Registers for A and B Buses

• Non-Inverting

• Three-State Outputs

• Drives 15 LSTTL Loads

• Typical Propagation Delay = 12ns (A to B, B to A) at

• Fanout (Over Temperature Range)

- Standard Outputs . . . . . . . . . . . . . . . 10 LSTTL Loads

- Bus Driver Outputs . . . . . . . . . . . . . 15 LSTTL Loads

• Balanced Propagation Delay and Transition Times

• Significant Power Reduction Compared to LSTTL

Logic ICs

• HC Types

- 2V to 6V Operation

Pinout

CD74HC646

(SOIC)

TOP VIEW

Description

The CD74HC646 is an octal bus transceiver/register with

three-state non-inverting outputs. This device is a bus

transceiver with D-type flip-flops which act as internal storage

registers. Data on the A bus or the B bus can be clocked into

the registers on the Low-to-High transition of either CAB or

CBA clock inputs. Outputs enable (OE) and direction (DIR)

inputs control the transceiver functions. Data present at the

high impedance output can be stored in either register or both

but only one of the two buses can be enabled as outputs at

any one time. The select controls (SAB and SBA) can

multiplex stored and transparent (real time) data. The

direction control determines which data bus will receive data

when the output enable (OE) is Low. In the high impedance

mode (output enable High), A data can be stored in one

register and B data can be stored in the other register. The

clocks are not gated with the direction (DIR) and output

enable (OE) terminals; data at the A or B terminals can be

clocked into the storage flip-flops at any time.

1

2

3

4

5

6

7

8

9

10

11

12

CAB

SAB

DIR

A0

A1

A2

A3

A4

A5

A6

A7

GND

16

17

18

19

20

21

22

23

24

15

14

13

SBA

OE

B0

B1

B3

B5

B6

B7

CBA

B2

B4

Ordering Information

PART NUMBER

TEMP.

PACKAGE

CD74HC646M

-55 to 125

24 Ld SOIC

CD74HC646M96

-55 to 125

24 Ld SOIC

NOTE: When ordering, use the entire part number. The suffix 96

denotes tape and reel.

January 1998 - Revised May 2003

CAUTION: These devices are sensitive to electrostatic discharge. Users should follow proper IC Handling Procedures.

Copyright

CD74HC646

High-Speed CMOS Logic

Octal Bus Transceiver/Register, Three-State

NOT

RECOMMENDED

FOR

NEW

DESIGNS