TC74HC646AP

2007-10-01

2

IEC Logic Symbol

Truth Table

G

DIR

CAB

CBA

SAB

SBA

A

B

Function

X

(Note)

X

(Note)

X

X

Inputs

Z

Inputs

Z

The output functions of A and B busses are

disabled.

H

X

X

X

X

X

Both A and B busses are used as inputs to the

internal flip-flops. Data on the bus will be stored

on the rising edge of the clock.

X

X

(Note)

L

X

Inputs

L

H

Outputs

L

H

The data on the A bus are displayed on the B bus.

X

(Note)

L

X

L

H

L

H

The data on the A bus are displayed on the B bus,

and are stored into the A storage flip-flops on the

rising edge of CAB.

X

X

(Note)

H

X

X

Qn

The data in the A storage flip-flops are displayed

on the B bus.

L

H

X

(Note)

H

X

L

H

L

H

The data on the A bus are stored into the A

storage flip-flops on the rising edge of CAB, and

the stored data propagate directly onto the B bus.

X

(Note)

X

(Note)

X

L

Outputs

L

H

Inputs

L

H

The data on the B bus are displayed on the A bus.

X

(Note)

X

L

L

H

L

H

The data on the B bus are displayed on the A bus,

and are stored into the B storage flip-flops on the

rising edge of CBA.

X

(Note)

X

(Note)

X

H

Qn

X

The data in the B storage flip-flops are displayed

on the A bus.

L

L

X

(Note)

X

H

L

H

L

H

The data on the B bus are stored into the B

storage flip-flops on the rising edge of CBA, and

the stored data propagate directly onto the A bus.

X: Don’t care

Qn: The data stored into the internal flip-flops by most recent low to high transition of the clock inputs.

Z: High impedance

Note:

The clocks are not internally gated with either G or DIR. Therefore, data on the A and/or B busses may be

clocked into the storage flip-flops at any time.