Interrupt-driven keyboard for MCS-51 uses few components

Designers of microcontroller-based products that require a keypad for user data entry can select from dedicating an input line for each key, continuously polling the keypad's x and y lines, or generating an interrupt whenever a user presses a key. The third method, an interrupt-driven keypad, offers several benefits. First, using interrupts frees the microcontroller to perform other tasks or to switch into an idling or power-down mode while awaiting the next key closure. Second, using interrupts helps reduce electromagnetic interference produced by continuously scanning the keypad's lines. The microcontroller's software returns a binary-formatted input corresponding to the pressed key's number. However, recovery from power-down mode to active mode to active mode normally requires a hardware reset.