Keypad Transmission

The program reads the character corresponding to the one pressed on the 4x4 keypad and transmits the character pressed on to the screen. The program sets up the keyboard matrix by configuring the columns as inputs and rows as outputs. It iterates through the rows, setting each to low and in turn checking the corresponding columns to see if they are set to 0. When both the column and row are set to 0, this means that the key is pressed. When a key is pressed, the program transmits the corresponding character on the keypad to the USART data visualizer. This is accomplished repeatedly as the main loop constantly scans for a key press.

#define F_CPU 16000000UL // 16MHz clock from the debug processor

#define BAUD 9600 // set the baud rate to 9600

#define BAUDRATE ((F_CPU/(16UL*BAUD)) - 1) // calculate the baudrate

#include <avr/io.h> // library to be able to use the functions

#include <util/delay.h> // time delay library

#include <string.h> // include string library

char Keyboard[4][4] = { {'1', '2', '3', 'A'}, 

      {'4', '5', '6', 'B'}, 

      {'7', '8', '9', 'C'}, 

      {'*', '0', '#', 'D'}   

};

void USART_initialize() {

// clear the high bits because they are not needed for this lab. Don't need that many bits

UBRR0H = (BAUDRATE>>8);

UBRR0L = BAUDRATE; // set the Low byte register to the BAUDRATE

UCSR0B |= (1<<TXEN0); // enable the receiver and transmitter

UCSR0C |= (1<<UCSZ00) | (1<<UCSZ01); // set to 8 bit data format

// don't need to set the stop bit since it is 1 by default

}

void Transmit(char strChar) {

// Wait for empty transmit buffer (isolates the 5th bit)

while ( !( UCSR0A & (1<<5) ) ) {}

UDR0 = strChar; // transmit the character 

}

char initialize_Rows_and_Columns() {

for (int i = 0; i < 4; i++){ // iterate though PB0 - PB4

DDRB &= ~(1 << i); // sets columns as input

PORTB |= (1 << i); // set the columns as the pull up

}

for (int i = 4; i < 8; i++) { // iterate though PD4 - PD7

DDRD |= (1 << i); // sets rows output

PORTD |= (1 << i); // set the rows as high (default)

}

}

char keyboard_scan() {

for (int i = 4; i < 8; i++){

PORTD &= ~(1 << i); // set the rows low one at a time and then check each column:

for (int j = 0; j < 4; j++) { // iterate through each column 

if ((PINB & (1 << j)) == 0) { // check which column is pulled low

// transmit the pressed key character to the screen

Transmit(Keyboard[i-4][j]);

// busy while, waiting for another key press to leave the if condition

while ((PINB & (1 << j)) == 0);

}}

PORTD |= (1 << i);

}}

int main(void){

USART_initialize();

initialize_Rows_and_Columns();

    while (1) {

keyboard_scan(); // constantly check if a key has been pressed

    }

}

 External Hardware Connections:

The FT232R Breakout board and the Atmel Xplained Mini board were utilized. Pin PD1 on the Atmel board was connected to the TXD pin on the FT232R board using a wire to set up the transmission. The grounds of both boards were also connected. Lastly, the keypad was connected to the AVR microcontroller. Pins PD3-PD7 were used to represent the rows and PB0-PB3 were used to represent the columns of the keypad.