TRUTH TABLE

INPUTS

OUTPUS

FUNCTION

CCLR LOAD

ENP

ENT

CCK

RCLR

RCK

R/C

G

QA

QB

QC

QD

XXX

X

XXXX

X

Z

Z

Z

Z

HIGH IMPEDANCE

L

X

X

X

(*)

X

X

L

L

L

L

L

L

CLEAR COUNTER

H

L

X

X

X

X

L

L

a

b

c

d

LOAD COUNTER

H

H

L

X

X

X

L

L

NO CHANGE

NO COUNT

H

H

X

L

X

X

L

L

NO CHANGE

NO COUNT

H

H

H

H

X

X

L

L

COUNT UP

COUNT UP

H

X

X

X

X

X

L

L

NO CHANGE

NO COUNT

X

X

X

X

X

L

(*)

H

L

L

L

L

L

CLEAR REGISTER

X

X

X

X

X

H

H

L

a’

b’

c’

d’

LOAD REGISTER

X

X

X

X

X

H

H

L

NO CHANGE

NO LOAD

(*) : X for HC690/691

for HC692/693

X : DON’T CARE

Z : HIGH IMPEDANCE

a-d : THE LEVEL OF STEADY STATE INPUTS AT INPUTS A THROUGHT D RESPECTIVELY.

a’-d’ : THE LEVEL OF STEADY STATE OUTPUTS AT INTERNAL COUNTER OUTPUTS a’ through qd’ respectively

HC690/692 RCO = QA

• QD • ENT

HC691/693 RCO = QA

• QB • QC • QD • ENT

BLOCK DIAGRAM

M54/M74HC690/691/692/693

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