How to Interface Keypad with AVR Slicker

Interfacing keypad with AVR Slicker

Tags: Interfacing keypad with AVR, Circuit Diagram to Interface keypad with AVR,C Program to 4 X 4 matrix keypad using AVR, source code to interface keypad with AVR microcontrollers,
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AVR Slicker Board

The AVR Slicker board is specifically designed to help students to master the required skills in the area of embedded systems. The kit is designed in such way that all the possible features of the microcontroller will be easily used by the students. The kit supports In-system programming (ISP) which is done through Parallel/Printer port.

ATMEL’s AVR (Atmega8535), AVR Slicker Kit is proposed to smooth the progress of developing and debugging of various designs encompassing of High speed 8-bit Microcontrollers.


A keypad is a set of buttons arranged in a block or "pad" which usually bear digits, symbols and usually a complete set of alphabetical letters. If it mostly contains numbers then it can also be called a numeric keypad. Here we are using 4 X 4 matrix keypad.

Interfacing keypad

Fig. 1 shows how to interface the 4 X 4 matrix keypad to two ports in microcontroller. The rows are connected to an output port and the columns are connected to an input port.

To detect a pressed key, the microcontroller grounds all rows by providing 0 to the output latch, and then it reads the columns. If the data read from the columns is D3-D0=1111, no key has been pressed and the process continues until a key press is detected. However, if one of the column bits has a zero, this means that a key press has occurred. For example, if D3-D0=1101, this means that a key in the D1 column has been pressed.

After a key press is detected, the microcontroller will go through the process of identifying the key. Starting with the top row, the microcontroller grounds it by providing a low to row D0 only; then it reads the columns.

If the data read is all 1s, no key in that row is activated and the process is moved to the next row. It grounds the next row, reads the columns, and checks for any zero. This process continues until the row is identified. After identification of the row in which the key has been pressed, the next task is to find out which column the pressed key belongs to.


Fig. 1 Interfacing keypad to Microcontroller

Interfacing keypad with AVR Slicker

We now want to scan a keypad in AVR Slicker Board. In case of 4X4 matrix Keypad both the ends of switches are connected to the port pin i.e. four rows and four columns. So in all sixteen switches have been interfaced using just eight lines.

1Keypads arranged by matrix format, each row and column section pulled by high or low by selection J15, all row lines(PORTB.0 – PORTB.3) and column lines(PORTB.4 to PORTB.7) connected directly by the port pins.

Pin Assignment with AVR Slicker






Connect PORTB with J15 (Key-pad) via FRC Cable

Turn ON TXD and RXD Pins of CONFIG-I switch SW24.

Connect Serial cable between

USART Section in the Board and PC and open HyperTerminal

Press RESET once.

Press a Key (Keypad) and the number will be displayed in HyperTerminal

















Circuit Diagram to Interface keypad with AVR


Source Code

The Interfacing keypad with AVR program is very simple and straight forward, that scan a keypad rows and columns. When the rows and columns are detected then it will display in PC through UART0. The C programs are developed in CodeVisionAVR software.

C Program to 4 X 4 matrix keypad using AVR


Title : Program to keypad interfacing







#define TXIF UCSRA.5


#define FOSC        16000000L   //Oscillator Frequency   16Mhz

#define USART_Baud  9600                                                

#define BaudH  ((unsigned int)(((FOSC/16/USART_Baud)-1) >> 8))

#define BaudL  ((unsigned int)(((FOSC/16/USART_Baud)-1) & 0xFF))


void Serial_init(void);

void ScanCol(void);

void ScanRow(void);


unsigned char Col=0,Row=0;

unsigned char Count[4][4]={0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};

unsigned char KeyArray[4][4]= { '1','2','3','4',



                                'D','E','F','0' };


void main()
















    printf("[%c]:Key Entry:%d\n\r",KeyArray[Row][Col],Count[Row][Col]);





void ScanRow()


    switch(PINB & 0x0f)


       case 0x07:Row=3;break;

       case 0x0b:Row=2;break;

       case 0x0d:Row=1;break;

       case 0x0e:Row=0;break;




void ScanCol()


    switch(PINB & 0xf0)


                case 0x70:Col=3;break;

                case 0xb0:Col=2;break;

                case 0xd0:Col=1;break;

                case 0xe0:Col=0;break;




void Serial_init(void)


        UCSRA = 0x00;    //Status Register

        UCSRB = 0x18;    //Transmit Enable,Receive

                         //enable,interrupts disabled   

        UCSRC = 0x86;    //8 databits,no parity,single stop   

        UBRRH = BaudH;

        UBRRL = BaudL; 


        printf("Press Anyone Key:\n\r");       



#define _ALTERNATE_PUTCHAR_       

void putchar(unsigned char Data)


   UDR = Data;     



To compile the above C code you need the CodeVision AVR software. The software has it’s own IDE and built-in AVR gcc- Compiler. They must be properly installed and a project with correct settings must be created in order to compile the code. To compile the above code, the C file must be added to the project.

In CodeVision AVR software, you can develop or debug the project without any hardware setup. You must compile the code for generating HEX file. In debugging Mode, you want to check the port output without microcontroller Board.

The AVR Code Blaster software is used to download the hex file into your microcontroller through Parallel port.

Testing the Keypad with AVR

Give +12V power supply to AVR Slicker Board; the serial cable is connected between the AVR Slicker Board and PC.

Open the Hyper Terminal screen, select which port you are using and set the default settings. Now the screen should show some text messages & it display which key is pressed in keypad.

If you are not reading any text from UART0, then you just check the serial cable is working. And also check the keypad keys are properly working or not. Otherwise you just check the code with debugging mode in CodeVision AVR.

General Information

  • For proper working use the components of exact values as shown in Circuit file. Wherever possible use new components.
  • Solder everything in a clean way. A major problem arises due to improper soldering, solder jumps and loose joints.
  • Use the exact value crystal shown in schematic.
  • More instructions are available in following articles,
       -  User Manual of AVR Slicker Board.
       -  How to create & Debug a Project in CodeVision AVR.

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