M74LCX646

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Table 3: Truth Table

X : Don’t Care

Z : High Impedance

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

* : The data at the A and B bus will be stored to the internal flip-flops on every low to high transition of the clock inputs.

G

DIR CAB CBA SAB SBA

A

B

FUNCTION

HX

INPUTS

INPUTS

Both the A bus and the B bus are inputs

X

X

X

X

Z

Z

The Output functions of the A and B bus are disabled

X

X

INPUTS

INPUTS

Both the A and B bus are used as inputs to the internal

flip-flops. Data at the bus will be stored on low to high

transition of the clock inputs.

LH

INPUTS

OUTPUTS The A bus are inputs and the B bus are outputs

XX*

L

X

LL

The data at the A bus are displayed at the B bus

HH

X*

L

X

L

L

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

data of the A bus are stored to internal flip-flop on low

to high transition of the clock pulse

HH

XX*H

X

X

Qn

The data stored to the internal flip-flop are displayed at

the B bus.

X*

H

X

L

L

The data at the A bus are stored to the internal flip-flop

on low to high transition of the clock pulse. The states

of the internal flip-flops output directly to the B bus.

HH

LL

OUTPUTS

INPUTS

The B bus are inputs and the A bus are outputs.

X*

X

X

L

LL

The data at the B bus are displayed at the A bus

HH

X*

X

L

L

L

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

data of the B bus are stored to the internal flip-flop on

low to high transition of the clock pulse.

HH

X*

X

X

H

Qn

X

The data stored to the internal flip-flops are displayed

at the A bus

X*

X

H

L

L

The data at the B bus are stored to the internal flip-flop

on low to high transition of the clock pulse. The states

of the internal flip-flops output directly to the A bus.

HH