Many applications require d r iving LEDs along with an inter face to a keypad. Implementing such designs usually i nvol ves using up significant amounts of the processors I/O lines. This application note desc r ibes a method which uses only 16 I/O pins of a PIC16C5X microcontroller to sample a 4x4 keypad matr ix, and directly dr ive four 7-segment LEDs (Figur e 1) . AN529 Multiplexing LED Drive and a 4x4 Keypad Sampling drive of the LEDs is possible, because of the high sink Author: Stan D’Souza and source capabilities of PIC16C5X microcontroller, Microchip Technology Inc. thus eliminating the use of an external drive transistor, and results in a reduction in both cost and complexity of INTRODUCTION the overall circuit. Typically applications having LEDs a……