MM74C923 Keyboard Encoder - (AD15966)

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 of resistance to be used. Diodes are not needed in the switch array to eliminate phantom switching. The internal debouncing circuit requires a single external capacitor and can also be connected bypassing the capacitor. The data available output goes to a high level when a valid keyboard input has been made. The data available output returns to a low level when the entered key has been released, even if another key is pressed. The data available will go high again to indicate acceptance of the new key after a normal debouncing period; this two-key action is provided between two switches. An internal register remembers the last key pressed, even after the key is released. The 3-state output allows for easy expansion and bus operation and is LPTTL compatible.

Datasheet