M74HC123 查看數據表（PDF） - STMicroelectronics
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M74HC123 Datasheet PDF : 14 Pages
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M54/M74HC123/123A
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-
pends on VCC and Cx.
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
quicky to VCC. This means if CL input goes low, the
IC becomes waiting state both in operating and non
operating state.
TRUTH TABLE
INPUTS
A
B
CL
H
H
X
L
H
H
X
H
L
H
L
H
X
X
L
X: Don’t Care Z: High Impedance
OUTPUTS
Q
Q
L
H
L
H
L
H
NOTE
OUTPUT ENABLE
INHIBIT
INHIBIT
OUTPUT ENABLE
OUTPUT ENABLE
INHIBIT
INPUT AND OUTPUT EQUIVALENT CIRCUIT
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