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M74HCT646M1R

HCT648 OCTAL BUS TRANSCEIVER/REGISTER (3-STATE, INV.) HCT646 OCTAL BUS TRANSCEIVER/REGISTER (3-STATE)

STMicroelectronics 

M74HCT646/648

TRUTH TABLE

HCT646 (The truth table for HCT648 is the same as this, but with the outputs inverted)

G DIR CAB CBA SAB SBA

A

B

FUNCTION

INPUTS INPUTS Both the A bus and the B bus are inputs

XXXX

Z

Z

The output functions of the A and B bus are disabled

HX

X X INPUTS INPUTS Both the A and B bus are used for inputs to the

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

low to high transition of the clock inputs

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

X X* L X

L

L

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

H

H

LH

X* L X

L

H

L

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

H

The data of the A bus are stored to the internal

flip-flop on low to high transition of th clock pulse.

X X* H X

X

X* H X

L

H

Qn

The data stored to the internal flip-flop are dispayed

at the B bus

L

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

H

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

states of the internal flip-flops output directly to the

B bus

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

X* X X L

L

H

L

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

H

X*

LL

XL

L

H

L

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

H

The data of the B bus are stored to the internal flip-

flop on low to high transition of the clock pulse

X* X X H

Qn

X

The data stored to the internal flip-flops are

displayed at the B bus

x*

XH

L

L

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

H

H

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

states of the internal flip-flops output directly to the

A bus

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

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