Overview

Product details

    The XL74C922 key encoder provides all the necessary logic to fully encode the SPST switch array. Keypad scanning can be accomplished with an external clock or external capacitors. These encoders also have on-chip pull-up devices, allowing the switches to use resistors up to 50 kΩ. No diodes are required in the switch array to eliminate ghost switching. The internal de-energizing circuit requires only one external capacitor, and can be defeated by omitting the capacitor. When a valid keyboard input is present, the Data Available output goes to a high level. When the entered key is released, the Data Available output returns to a low level, even if another key is pressed. Data Available will return high to indicate acceptance of a new key after the normal unload period; this double key rollback is provided between any two switches.