Lab 3 Introduction to MEGA 2560 Board and I/O Instructions

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Lab 3 Introduction to MEGA 2560 Board and I/O Instructions
Submit lab3BlinkOne.asm at the end of your lab, not your project.
I. I/O Instructions
In the AVR MEGA 2560 microcontroller, each Input/Output (I/O) port has three associated
registers, the data direction register (DDRx), output register (PORTx), and input register
(PINx). These registers correspond to addresses in the data space accessible by the processor
(the first 0x200 bytes in SRAM).
Launch AVR Studio 4 and observe the I/O View. Expand PORTB and PORTL
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Some ports are mapped to two addresses, for example, PORTB is mapped to 0x05 and 0x25,
you may use IN/OUT instructions to transfer data between registers and SRAM (data memory)
for address between 0x00 and 0x3F, but some ports such as PORTL are mapped to one
addresses which are bigger than 0x3F, they can’t be manipulated using the IN/OUT
instructions, what are we going to do? We use LDS and STS instructions instead. In AVR,
Ports A to G use Port Mapped I/O (separate addresses from memory) and Ports H to K use
Memory Mapped I/O (usage is similar to any memory location). Port Mapped addresses have
to use separate In/Out instructions while Memory mapped use LDS and STS.
II. Pins and Ports
The six LEDs are associated with six pins and the pins are mapped to some bits of two ports:
PORTB and PORTL:
Create a new project named lab3. Write a small program to turn a specific LED on. Type the
following code. Note that the I/O registers - 0x10B and 0x10A - are specified in hexadecimal
numbers. The two I/O registers are given names, PORTL and DDRL, by using the .equ
directives to the port numbers (the memory addresses in data memory). Once equated, the I/O
registers are referred to by names instead of numbers in the program.
Port L: bit 7 PL7
Port L: bit 5 PL5
Port L: bit 3 PL3
Port L: bit 1 PL1
Port B: bit 3 PB3
Port B: bit 1 PB1
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III. Build and download the .hex file to the board:
 Build the program above. Observe the changes of the registers and the I/O registers.
 Note to which COM port the lab AVR board is connected to. This is different on
each machine. You can check this by going to Start - Devices and Printers.
 In the above example, the Arduino Mega is on COM4. So please check the port
number of Arduino Mega on the machine you are currently working on.
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 Upload the lab3.hex file to the board by typing the following command at the
command window:
"C:\WinAVR\bin\avrdude" -C "C:\WinAVR\bin\avrdude.conf" -p atmega2560 -c
wiring -P COM4 -b 115200 -D -F -U flash:w:filename.hex
You may need to change the path and filename if the settings are different from this. Or,
download “upload.bat” file to the same directory where your lab3.asm program is stored.
Modify the com port (-P COM4) to reflect the one on your machine. Open a command
window get to the same directory where upload.bat is stored, and type upload.bat. “upload.bat”
is a batch file. It is another way to type a command. You need to change the file name if your
project is not called lab3. Learn some DOS command, such as “cd” – change directory.
IV. Exercises:
1. Change the number transferred to r19, rebuild the program and upload it to the board,
observe which LED is on. Change the number if you want to turn on the LEDs mapped to
pins 46, 44, 42. Change the code if you want to turn on the LEDs mapped to pins 50 and 52.
2. Download blinkOne.asm and change some of the code such that only one LED blinks.
Submit lab3BlinkOne.asm at the end of your lab.
This lab is derived from the Chapters 2 and 3 of your textbook (Some Assembly Required by
Timothy S. Margush)