MM74C922 Keyboard Encoder - (AD7307)

Description:

The MM74C922 and MM74C923 CMOS keyboard encoders provide all the necessary logic to fully encode an SPST switch array. Keyboard scanning can be implemented either by an external clock or an external capacitor. These encoders also have on-chip pull-up devices that allow switches with up to 50 KW in resistance to be used. No diodes are needed in the switch array to eliminate ghosting. The internal debounce circuit needs a single external capacitor and can also be connected by omitting the capacitor. The data available output goes high when a valid keyboard input has been made. The data available output returns low when the entered key has been released, even if another key is pressed. The data available will return high to indicate acceptance of the new key after a normal debounce period; this two-key action is provided between two switches. An internal register remembers the last key pressed, even after releasing the key. The 3-state outputs allow for easy expansion and bus operation and are LPTTL compatible.

Datasheet