Mark Neil - Microprocessor Course 1 Decoding and Using a 4x4 Keyboard

The Keyboard Mark Neil - Microprocessor Course 2 8 lines corresponding to 4 rows and 4 columns 8 lines corresponding to 4 rows and 4 columns By Pressing a button you connect one of the row lines to one of the column lines. By Pressing a button you connect one of the row lines to one of the column lines.

The PCB of the Key-Board Mark Neil - Microprocessor Course 3 The buttons simply connect one row with one column! From this picture you Can see that the keyboard is all PASSIVE: No ICs no Transistors From this picture you Can see that the keyboard is all PASSIVE: No ICs no Transistors

Decoding what key is pressed Step 1: Row We can provide power to the four rows, and readout the data We write 0 to all columns In the example on the right (the 5 is pressed) we will see a 0 on row 2 and 1 on the rest of the rows We then have to determine which column has been pressed 4 Mark Neil - Microprocessor Course

Step 2:Reading the Column If instead of providing power to the rows, we provide power to the columns we can determine which column has a key pressed We write 0 to all the rows In this case we will read 0 on column 1 and 1 on the other rows Hence we know that the ‘5’ was pressed as row 2 and col 1 have a key pressed 5 Mark Neil - Microprocessor Course

Pull-up Resistors on ATmeag128 Ports Mark Neil - Microprocessor Course 6 PORTx : OUTPUT Register DDRx : Direction Reg. PINx : INPUT (no Register) each pin in PORTx is independent! There are pull-up resistors present on-board. Which allow us to put power on the PORT pins. These need to be enabled by writing high levels to input pins.

Reading the Keypad with the ATMega128 Mark Neil - Microprocessor Course 7 We will use PORTE for both Reading the pins and providing the Power. This example is the initial configuration to read the row PORTE bits 4-7 Outputs PORTE bits 0-3 Inputs

Task Plan - Steps Mark Neil - Microprocessor Course 8 Enable the pull-up resistors on bits 0-3 of PORTE and connect the 4 pins of the keyboard. Configure these pins as inputs, the 4 lines will be held high by the pull-up resistors. Connect the rest of keyboard to pins 4-7 of PORTE and configure them as outputs. Write a program that drives the output bits (4-7) of PORTE low all at once read the 4 PORTE input pins (0-3).  Determine which row has a key pressed Now configure bits 0-3 as outputs and bits 4-7 as inputs  Determine which column has a key pressed Determine which key has been pressed Echo the PORTE input to PORTB to use the LEDs to do a quick check of the keyboard. [also output to LCD.]

How to configure PORTE for Step 1 Mark Neil - Microprocessor Course 9 To configure PORTE 4-7 as outputs and PORTE 0-3 as inputs  set DDRE:$F0 Set the PORT REGISTERS in such a way so that the inputs have pull up resistors and the outputs drive low  set PORTE:$0F

Task Mark Neil - Microprocessor Course 10 Write a routine that decodes the key on the 4x4 Keyboard and tells you what key was pressed on the LCD display We need a reliable setup where the ATmega128 interprets relatively quickly any key pressed on the keyboard. Notice that the microprocessor is faster than your finger and can ‘see’ the bouncing up and down that happens when you press the a button of the keyboard.  Write a routine which reliably inputs a key press.  Write a routine which reliably inputs a string of key presses