TLF6037

July 1993

MM54C922MM74C922 16-Key Encoder

MM54C923MM74C923 20-Key Encoder

General Description

These CMOS key encoders provide all the necessary logic

to fully encode an array of SPST switches The keyboard

scan can be implemented by either an external clock or

external capacitor These encoders also have on-chip pull-

up devices which permit switches with up to 50 kX on resist-

ance to be used No diodes in the switch array are needed

to eliminate ghost switches The internal debounce circuit

needs only a single external capacitor and can be defeated

by omitting the capacitor A Data Available output goes to a

high level when a valid keyboard entry has been made The

Data Available output returns to a low level when the en-

tered key is released even if another key is depressed The

Data Available will return high to indicate acceptance of the

new key after a normal debounce period this two-key roll-

over is provided between any two switches

An internal register remembers the last key pressed even

after the key is released The TRI-STATE

outputs provide

for easy expansion and bus operation and are LPTTL com-

patible

Features

Y

50 kX maximum switch on resistance

Y

On or off chip clock

Y

On-chip row pull-up devices

Y

2 key roll-over

Y

Keybounce elimination with single capacitor

Y

Last key register at outputs

Y

TRI-STATE outpust LPTTL compatible

Y

Wide supply range

3V to 15V

Y

Low power consumption

Connection Diagrams

Pin Assignment for

Dual-In-Line Package

TLF6037 – 1

Top View

Order Number MM54C922 or

MM74C922

Pin Assignment

for SOIC

TLF6037 – 14

Top View

Order Number MM74C922

Pin Assignment for

DIP and SOIC Package

TLF6037 – 2

Top View

Order Number MM54C923 or

MM74C923

TRI-STATE

is a registered trademark of National Semiconductor Corporation

C1995 National Semiconductor Corporation

RRD-B30M105Printed in U S A