FUNCTIONAL DESCRIPTION (continued)

RE-TRIGGERED OPERATION

When a second trigger pulse follows the first its ef-

fect will depend on the state of the multivibrator. If

the capacitor Cx is being charged the voltage level

of R/C external falls to Vrefl again and Q remains

high i.e. the retrigger pulse arrives in a time shorter

than the period Rx

⋅ Cx seconds, the capacitor

charging time constant. If the second trigger pulse

is very close to the initial trigger pulse it is ineffective

; i.e. the second trigger must arrive in the capacitor

discharge cycle to be ineffective; Hence the mini-

mum time for a second trigger to be effective de-

RESET OPERATION

CL is normally high. If CL is low, the trigger is not ef-

fective because Q output goes low and trigger con-

trol flip-flop is reset.

Also transistor Op is turned on and Cx is charged

IC becomes waiting state both in operating and non

operating state.

TRUTH TABLE

INPUTS

OUTPUTS

NOTE

AB

CL

Q

Q

H

H

OUTPUT ENABLE

X

L

H

L

H

INHIBIT

H

X

H

L

H

INHIBIT

L

H

OUTPUT ENABLE

L

H

OUTPUT ENABLE

X

X

L

L

H

INHIBIT

X: Don’t Care Z: High Impedance

INPUT AND OUTPUT EQUIVALENT CIRCUIT

M54/M74HC123/123A

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