Department of Electrical and Electronic Engineering

EIE373 Microcontroller Systems and Interface

Laboratory Exercise 4: AVR Serial Port Programming

Objective:

To develop C programs with serial port communication under the Arduino platform.

Introduction:

This experiment introduces an application  for serial port communication inside the AVR microcontroller.

Equipment:

Atmel Studio

The Arduino Starter Kit

Procedure:

Section A: Write a C program to echo a character

Write a C program to complete the following task:

Receive a character from the serial port by using the polling method and then send it to a PC terminal through the serial port. The baud rate should be 4800.

To view the serial port communication, you should use the freeware “Tera Term,” a PC terminal. You can locate this software on your computer using the search function.

Select “Serial” and an appropriate port for the serial port communication. The port number should be the same as the port the Arduino connects to your computer.

Select “Setup” from the main menu and then “Serial port” . Set the baud rate to 4800.

Important information:

Note that you must close Tera Term before you burn your program into Arduino; otherwise, Tera Term holds the serial port, and you cannot burn your program successfully.

A character can be sent to the Arduino by typing it (i.e., using the keyboard). When you type a character, Tera Term gets the input and sends it to the Arduino through the serial port. When the Arduino receives a character, it will send it to the serial port, and you can read it through Tera Term.

Section B: Write a C program to send and receive strings

Write a C program to complete the following tasks:

1.   (Do it once at the beginning) Send “We Are Ready” to the serial port using polling. Note that the clock frequency of the Arduino Start Kit is 16 MHz.

2.   (Do it repeatedly) Receivedata from the serial port by polling. If the received string is “Hi”, your program should send “Bye” to the serial port. (Hint: To get a string from the serial port, your program should receive it character by character. For example, if your program gets a string “abc”, the characters received from the serial port should be “a” first, and then “b”, and finally “c”.)

The string “Hi” can be sent to the Arduino by typing it (i.e., using the keyboard) in Tera Term. When you type “Hi”, Tera Term gets the input and sends it to the Arduino through the serial port. When the Arduino receives the string, it will send a message “Bye!” to the serial port, and you can read it through Tera Term (see the figure below):

Section C: Write a C program to keep sending and receiving characters

Write a C program to complete the following tasks using the polling method:

1.   Before you press any keys, the character ‘a’ is printed continuously.

2.   When you press a key (say ‘b’), ten characters of this key (i.e., ‘b’) are printed out and then stop.

3.   After that, nothing happens when you press a key other than the first key (i.e., ‘b’).

4.   When you press the key again (i.e., ‘b’), the character ‘a’ is printed continuously (i.e., resume).

Set the baud rate of the PC terminal (i.e., Tera Term) to 9600.

If your program runs successfully and the setting of Tera Term is correct, you should see the following output:

Section D: Write C programs by using the serial port interrupt

You should repeat Sections B and C, but this time, you should use the serial port interrupt (not the polling method).