74ABT646A_3

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Product data sheet

Rev. 03 — 15 March 2010

5 of 19

NXP Semiconductors

74ABT646A

Octal bus transceiver/register; 3-state

6.

Functional description

[1]

H = HIGH voltage level;

L = LOW voltage level;

X = don’t care;

↑ = LOW-to-HIGH clock transition;

[2]

The data output function may be enabled or disabled by various signals at the OE input. Data input functions are always enabled,

i.e. data at the bus pins will be stored on every LOW-to-HIGH transition of the clock.

Table 3.

Function table[1]

Inputs

Data I/O

Operating mode

OE

DIR

CPAB

CPBA

SAB

SBA

An

Bn

XX

↑

X

X

X

input

unspecified

output[2]

store A, B unspecified

XXX

↑

X

X

unspecified

output[2]

input

store B, A unspecified

HX

↑↑

X

X

input

input

store A and B data

H

X

H or L

H or L

X

X

input

input

isolation, hold storage

L

L

XXXL

output

input

real time B data to A bus

L

L

X

H or L

X

H

output

input

stored B data to A bus

L

H

X

X

L

X

input

output

real time A data to B bus

L

H

H or L

X

H

X

input

output

stored A data to B bus