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74C922-SO IC Keyboard Encoder for up to 16 switches MM74C922 Replacement IC

General Description

The 74C922-SO is designed as a replacement chip for the obsolete MM74C922 surface mount part. The 74C922-SO contains all the logic necessary to encode a SPST keyboard switch array up to 4 by 4 in size and provide a 4 bit parallel output and a data available signal. The data available signal goes high when a key is pressed, and goes low before another key output is generated. The data output pins keep their state even after the key is released. The array can be a 4 x 4 array, but smaller arrays such as a 3 x 4 array or any smaller size can be used. The 74C922-SO handles debouncing of the keys as well. No external capacitors are required for timing; all timing is internally generated. No external diodes are required in the array to prevent key ghosting in a two key rollover situation. A .1 uF bypass capacitor is suggested across the VDD and VSS pins. The part uses the standard 20 pin .3 inch width SOIC and DIP package.

Features:

  • Replacement Chip for MM74C922
  • Fully encodes a key switch array. (up to 4 x 4)
  • No external parts required.
  • Low power consumption 1.5 mA typical.
  • Supply voltage 2.4 to 5.25 volts.
  • Last key pressed retained on data outputs.
  • All timing internally generated.
  • 2 Key rollover.
  • On chip row input resistors.
  • Internal key bounce elimination.
  • TTL and CMOS compatible outputs.
  • Part is in full production.
  • SOIC and DIP 20 Pin Package.
  • Low EMI.
  • ROHS Compliant.

Example Circuit

Spec sheet: Keyboard Encoder parallel output 16 keys 74C922-SO

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