This is as simple routine how to read 4x4 keypad keys using AVR-GCC language. The keypad is connected to AVR microcontroller 8 bit port. In this example it is B port. You can change ports depending on your needs – this is only an example ant it is not the only way to this.
Howt it works. Well very simply. PORTB is divided into two nibbles PINB0 – PINB3 as inputs (as rows) and PINB4-PINB7 as outputs (columns). The keys are checked in a loop in series. Lets say if we set first row output (PORTB bit 7) to 0 then when checking rows we are looking which bit is set to 0, because of key pressed with function bit_is_set(PINB, bitNo). This function gives non-zero if bit is clear.
10k resistors protect AVR from shortcuts.
#include <avr/io.h> int main() { //high nibble for output(columns) low for input(rows); DDRB=0xF0; //enable internal pullups for PB0-PB3 PORTB=0x0F; //Port D for indication only DDRD=0xFF; while (1) //loop key check forever { //first column PORTB =0b01111111; //check for rows and send key number to portD //instead sending key number to PORTD you can use // any function that serves pressed button if (bit_is_set(PINB, 3)) PORTD=1; if (bit_is_set(PINB, 2)) PORTD=2; if (bit_is_set(PINB, 1)) PORTD=3; if (bit_is_set(PINB, 0)) PORTD=4; //second column PORTB =0b10111111; if (bit_is_set(PINB, 3)) PORTD=5; if (bit_is_set(PINB, 2)) PORTD=6; if (bit_is_set(PINB, 1)) PORTD=7; if (bit_is_set(PINB, 0)) PORTD=8; //third column PORTB =0b11011111; if (bit_is_set(PINB, 3)) PORTD=9; if (bit_is_set(PINB, 2)) PORTD=10; if (bit_is_set(PINB, 1)) PORTD=11; if (bit_is_set(PINB, 0)) PORTD=12; //fourth column PORTB =0b11101111; if (bit_is_set(PINB, 3)) PORTD=13; if (bit_is_set(PINB, 2)) PORTD=14; if (bit_is_set(PINB, 1)) PORTD=15; if (bit_is_set(PINB, 0)) PORTD=16; } }
