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.
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