Lab 4: AVR Hardware & Calculator with keypad input.

PART 1

In this lab we will be configuring your physical AVR microcontroller for the first time. Step 1 is to build the circuit below on your breadboard. For more information on pinout of the AVR microcontroller, see the AVR datasheet here. The datasheet will be your best friend for the rest of the quarter, so it would be useful to learn how to navigate it.

All resistances are 330 Ohms.

Step 2 is to configure your AVR for use for the first time. Open AVR Studio and start a new project following the protocol given in lab 1. Build the following code:

SAMPLE CODE:

#include "avr/io.h"

int main() {

DDRA = 0xFF;

while(1) {

PORTA = 0xAA;

}

Once the code above successfully compiles, select Tools->Program AVR->Connect to bring up the dialog box below. Ensure the below options are selected, and that your programmer is plugged into your machine via USB cable.

Click connect in the above dialog, and the below dialog should pop up. Ensure that the ATMega32 device is selected, and that ISP programming mode is selected.

Click the board tab, and change the ISP frequency to 125 KHz and press write.
Now click the fuses tab and select "Int. RC Osc 8 MHz: 6 CK + 64ms", also ensure that "JTAG Interface Enabled" is UNCHECKED. Select program.
Click the lockbits tab and ensure that "Mode 1" is selected throughout the list. Great! now you are are ready to program the board for the first time. Go back to the main dialog page by clicking the program tab.
Click the ellipses in the FLASH memory (We will not be using EEPROM in this class), and select the .hex file that should have been generated when you built the project (it is typically found in project_dir/default directory). Now select the program button and voila! You should have some lights on the breadboard lit up.

Part 2

Lab 3 we will be implementing a simple calculator with 4 functions. We will use the keypad as input to the design. You must use the state machine format provided in lab 3 to implement your design, and a large percentage of your grade will depend on you using the correct format. Remember that this is a course in embedded system DESIGN, as well as in programming, thus you should have a complete state machine design in pen and paper BEFORE you start to write code.

Here is how a user should be able to use the calculator.

A number is entered which represents the first argument of the expression to calculate. The number is shown on the LEDs for verification
A letter A-D is selected which represents the function to perform. A 1,2,3,4 should be displayed that corresponds to the correct function.

A -Add
B - Subtract
C - Multiply
D - Divide

A second number is entered which represents the second argument of the expression. The number is shown on the LEDs for verification
The '#' sign is entered to signify that the expression has been entered and is ready to be calculated.
The output is shown on the LEDs connected to port A.

KEYPAD INPUT

Keypads are often used as a primary input device for embedded microcontrollers. The keypads actually consist of a number of switches, connected in a row/column arrangement as shown below

In order for the microcontroller to scan the keypad, it outputs a nibble to force one (only one) of the columns low and then reads the rows to see if any buttons in that column have been pressed. The rows are pulled up by the internal weak pull-ups in the AVR ports. Consequently, as long as no buttons are pressed, the microcontroller sees a logic high on each of the pins attached to the keypad rows. The nibble driven onto the columns always contains only a single 0. The only way the microcontroller can find a 0 on any row pin is for the keypad button to be pressed that connects the column set to 0 to a row. The controller knows which column is at a 0-level and which row reads 0, allowing it to determine which key is pressed. For the keypad, the pins from left to right are: R1, R2, R3, R4, C1, C2, C3, C4.

Below is the start of a function that you should use to get input from the keyboard. You will need to complete the function. The function would be most helpful if it returned an index into the following conversion table.

SAMPLE CODE:

/* You can have a conversion table to convert the key position into a

valid number which indicates the operator or operand value. For eg:

the numbers 0 to 9 are valid operands and 100 to 103 denote

addition, subtraction, multiplication and division respectively */

/* Note that your keypad has a different layout then the one used to

design this lab, thus you will need to edit the conversion table to

reflect your own keypad layout.*/

char conv_table[] =

{

1, 2, 3, 100 /* add */,

4, 5, 6, 101 /* sub */,

7, 8, 9, 102 /* mul */,

-1, 0, -1, 103 /* div */

};

int GetKey( ) {

for(i=0; i<4; i++) { /* Set one column at a time to 0. */

PORTC = 0xff & ~(1<<i);

for (j=4; j<8; j++) { /* Scan each row to see if a button was pressed */

/* Use i and j to index into conversion table */

}

PORT/PIN Registers (PORT is for writing! PIN is for reading!)

Note that when reading an input from the pins of an AVR, we use the PIN registers of the corresponding port (as opposed to PORT register). Thus to write a value x as an output to port C we would use the statement "PORTC = x", and to read an input value into a variable x on port d we would use the statement "x = PIND".
The nuanced difference between the PORT and PIN registers is that PIN register always reflects the current level on the pins of the microcontroller port (subject to both writing from software and voltage levels on the breadboard), whereas the PORT register will return only the last value that you wrote to it. This means that the breadboard hardware could change the logical level of the pins of the port, but the PORT register would not recognize that.

POST LAB

INDIVIDUALLY prepare and submit a single-spaced half page report with the following information.

I. Lab Objective
II. Personal Contributions
III. Skill learned & knowledge gained.

Turnin

INDIVIDUALLY prepare and submit all lab files into a tar ball. All .c files should be included in lab parts, as well as post lab submitted in pdf and txt format. All files should include a header with name, login, email, lab section, assignment, and group associates; also include: "I acknowledge all content is original."

For Example
Name: John Doe
Login: jdoe
Email: jdoe@cs.ucr.edu
Lab Section: 021
Assignment: Lab 4
Group: John Doe, Jane Doe, and Joe Doe
I acknowledge all content is original.

Tar ball command: tar -cvzf name.tgz *.c *.pdf *.txt

The tar command will compress all files into a .tgz file with all .c .pdf, and .txt files in that directory. Do not include unnecessary files! The .c files be named as follows lab#_part#.c and the postlab#.pdf/postlab#.txt.

For Example:
lab4_part1.c
lab4_part2.c
postlab4.pdf
postlab4.txt