PIC16F877 and 4×5 keypad

The circuit here described is a simple 45 keypad that can be used in particular with the PIC 16F877 microcontroller, for which it has been designed considering a supply of 5V, 16F877 I/O pins leakage current, the voltage level recognized as a high or low state while in TTL or ST mode, etc.. Since this circuit is quite simple, and the resistors’ value not critical, it should be suitable for other PICs and other microcontrollers, too.

PIC16F877 and 45 keypad: [Link]