September 1993

4

Philips Semiconductors

Product specification

Octal bus transceiver/register; 3-state

74HC/HCT646

Fig.4 Functional diagram.

FUNCTION TABLE

Notes

1. H = HIGH voltage level

L = LOW voltage level

X = don’t care

↑ = LOW-to-HIGH level transition

2. The data output functions may be enabled or disabled by various signals at the OE and DIR inputs. Data input

functions are always enabled, i.e., data at the bus inputs will be stored on every LOW-to-HIGH transition on the clock

inputs.

FUNCTION

OE

DIR

H

H

X

X

H or L

↑

H or L

↑

X

X

X

X

input

input

isolation

store A and B data

L

L

L

L

X

X

X

H or L

X

X

L

H

output

input

real-time B data to A bus

stored B data to A bus

L

L

H

H

X

H or L

X

X

L

H

X

X

input

output

real-time A data to B bus

stored A data to B bus