TLF6409

February 1992

DM74LS221 Dual Non-Retriggerable One-Shot

with Clear and Complementary Outputs

General Description

The DM74LS221 is a dual monostable multivibrator with

Schmitt-trigger input Each device has three inputs permit-

ting the choice of either leading-edge or trailing-edge trig-

gering Pin (A) is an active-low trigger transition input and

pin (B) is an active-high transition Schmitt-trigger input that

allows jitter free triggering for inputs with transition rates as

slow as 1 voltsecond This provides the input with excellent

noise immunity Additionally an internal latching circuit at the

clear (CLR) input can terminate the output pulse at a prede-

termined time independent of the timing components This

(CLR) input also serves as a trigger input when it is pulsed

with a low level pulse transition (

) To obtain the best

and trouble free operation from this device please read op-

erating rules as well as the NSC one-shot application notes

carefully and observe recommendations

Features

Y

A dual highly stable one-shot

Y

Y

Pin-out identical to ’LS123 (Note 1)

Y

Output pulse width range from 30 ns to 70 seconds

Y

Hysteresis provided at (B) input for added noise

immunity

Y

Direct reset terminates output pulse

Y

Triggerable from CLEAR input

Y

DTL TTL compatible

Y

Input clamp diodes

Note 1

The pin-out is identical to ’LS123 but functionally it is not refer to

Operating Rules

10 in this datasheet

Functional Description

The basic output pulse width is determined by selection of

the basic pulse width is independent of further input tran-

sitions and is a function of the timing components or it may

be reduced or terminated by use of the active low CLEAR

input Stable output pulse width ranging from 30 ns to 70

seconds is readily obtainable

Connection Diagram

Dual-In-Line Package

TLF6409 – 1

Order Number DM74LS221M or DM74LS221N

See NS Package Number M16A or N16A

Function Table

Inputs

Outputs

CLEAR

A

B

Q

Q

LX

X

L

H

XH

X

L

H

XX

L

L

H

HL

u

H

v

H

u

LH

e

A Positive Pulse

e

A Negative Pulse

This mode of triggering requires first the B input be set from a low to high

level while the CLEAR input is maintained at logic low level Then with the B

input at logic high level the CLEAR input whose positive transition from low

to high will trigger an output pulse

TLF6409 – 2

C1995 National Semiconductor Corporation

RRD-B30M105Printed in U S A