Lets Learn AVR - Step 1:

The first step in the development of any micrcontroller is to know about its architecture and instruction set. So i advice you all to keep a copy of instruction set and architecture manual. You can download them from the link below.
AVR Instruction Set (User Guide, 150 pages)
Architecture Manual or Datasheet for your AVR Microcontroller

The above document will help you to get familiar with the instruction set and to know about your AVR in a better way.
After this, we now have to decide the IDE on which you are going to work or write program for your AVR. I advice you to use AVR Studio 4 from Atmel Corporation, which is a free IDE for AVR and it has many features like programming, debugging etc.
You can get your free copy of AVR studio from link below.
AVR Studio 4.12 (build 460) (45 MB, updated 11/05) - Registration needed
AVR Studio 4.12 Service Pack 4 (build 498) (25 MB, updated 10/06) - No registration
AVR Studio 4.13 (build 528) (73 MB, updated 03/07) - Registration needed

So you can download any of the copy above as per your need more information about AVR studio can be obtained from
AVR Studio 4

All documents and IDE for writing program is ready.. only thing left is a programmer, with which we are going to program our AVR. As we know almost all AVR comes with ISP (In System Programmable) ports. So you don't need any special hardware to program your AVR. Please see the link below for ISP programmer for AVR.
Download PonyProg - serial device programmer

Interfacing Schematic:


Note: Do not forget to run the setup after installing PonyProg.

Setup Information:
In interface setup, select parallel and then from the drop down select AVR ISP I/O.
slect the LPT Port (parallel port) available on your PC. Then click ok!

To load Hex file:
Go to File-> Open Program (FLASH) file
then from the drop down where ".e2p" is show, select ".hex" and load your hex file.

AVR Tutorial - Step 2



Before programming AVR, first you need to know few important programming tips and AVR registers.


This include the definition file for ATmega8515, so that we can directly address the registers with their names.
All AVRs have 32 general purpose registers from R0 - R32.
R0-R15 registers have certain restrictions of use, i.e. they are not allowed to load immediate value.
e.g. LDI R15, $35
the above statement will give you an error, saying "Invalid Register"
Where as registers from R16-R32 can be used for this purpose i.e.
LDI R16,$35
is a valid statement.
You can move values from one register to other by using
MOV R15,R16

Not only the registers from R0 to R15 has restriction on LDI but also other commands where the use of R0-R16 is not allowed. usually all commands having immediate operands are not allowed.
For the ease of programming, you can also give names to the register like


There are some special registers like X,Y and Z for 16-Bit operations. They are used to read and write to XRAM. They are also used for reading from program memory like reading from a lookup table (we will discuss about them when we use them). These special registers are actually combination of two 8-bit General purpose registers. i.e. X is actually R26:R27, Y is R28:R29 and Z is R30:R31.
The lower byte of the 16-bit-adress is located in the lower register, the higher byte in the upper register. Both parts have their own names, e.g. the higher byte of Z is named as ZH (R31) and the lower Byte is ZL (R30). Similarly for X (XL and XH) and for Y (YL and YH). These names are defined in the standard header file for the chips (which we include while writing program). Dividing these 16-bit-pointer-names into two different bytes is done like follows:

where LABEL is address for any lookup table or any memory location.

Some important notes for using registers

1. Define names for registers with the .DEF directive, never use them with their direct name Rx. This helps you making better use of registers and you will never confuse yourself while using them.
   
2. If you need pointer access reserve R26 to R31 for that purpose.
   
3. 16-bit-counter are best located R25:R24.
   
4. If you need to read from the program memory, e.g. fixed tables, reserve Z (R31:R30) and R0 for that
   purpose.
   
5. If you plan to have access to single bits within certain registers (e.g. for testing flags), use R16 to
   R23 for that purpose

Now coming to ports, The information about a specific port of a certain type of AVR can be easily obtained in the AVR Datasheet. Port names are defined in the include file of the CPU..
if you don't have an include file then you can define yourself as..

So if you are not able to find an include file you can use the .EQU directive to define ports and other registers.
Making port as i/p or o/p is purely dependent on data direction register called DDRx (DDRA for port A etc.) The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written
logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured
as an input pin.
for writing and reading data to Ports, PORTx registers are there. and to read from ports PINx registers are there.
for example..
writing to port

Reading from port



We are finished with the basics of AVR, lets try programming with simplest program. Blinking an LED!



Please post your problems in the forum
Doubts in AVR tutorial

Lets learn AVR Tutorial - Step 3

In this part of tutorial you will learn

1. Reading from Program memory
   
2. Reading from RAM
   
3. Writing to RAM
   
4. Practice programs

Here is the summary of Load and store instructions that are used for dealing with SRAM of AVR Microcontroller

1. LD Rn,X/Y/Z
   >either X or Y or Z register can be used
   >this will load the value which is stored in memory location pointed by register X/Y/Z to the destination register Rn (can be R0, R1.. any etc)
   
2. LD Rn,X+/Y+/Z+
   >This instruction will load the value which is stored in memory at location pointed by X/Y/Z registers and then increment the memory location by 1
   >This is a post increment instruction
   
3. LD Rn, -X/-Y/-Z
   >Load Rn with value stored at location pointed by pre-decrement of address stored in X/Y/Z
   
4. LDD Rn,Y/Z+displacement
   >Load Rn with value at address Z or Y + displacement
   >e.g. Z is 0x0090, Displacement is 0x10 so Rn will be loaded with value stored at 0x0090+0x10 = 0x0100
   
5. ST X/Y/Z, Rn
   >Store the value of Rn to location pointed by X or Y or Z
   
6. ST X+/Y+/Z+, Rn
   >Store the value in Rn to location pointed by X or Y or Z and increment the address pointer
   
7. STD Y/Z+displacement, Rn
   >Store the value in Rn to location pointed by Y or Z + Displacement
   
8. LDS Rn, SRAM_Address
   >Load value from SRAM Address to the Rn register
   >SRAM Address is the immediate value e.g. LDS R0,0x0100
   
9. STS SRAM_Address, Rn
   >Store Rn to immediate SRAM location

To read from Program memory we have special instructions like

1. LPM
   >Load form program memory, This instruction is used in most of the AVRs and its hard coded in the architecture.
   >This instruction will load R0 with the address specified by register Z [This is hardcoded]
   
2. LPM Rn, Z
   >Load Rn from program memory pointed by register Z
   >This instruction is not supported by all AVRs e.g ATMega8515, AT90S8515
   
3. LPM Rn,Z+
   >Load Rn from program memory and increment the memory location pointed by Z
   >This instruction is also not supported by all AVRs

Note: load from program memory instructions are not supported by all AVR architectures. Most of the architectures support LPM instruction which is hard coded to load R0 from location in Z. where as in some AVR this is also not implemented.

Now we are done with the instructions overview.. now lets practice them..
Program 1: Copy 10 Bytes memory block stored in Program memory(ROM) to Data memory (SRAM)


Program 1: Find Greatest of 3 numbers Stored in program memory


Now you can try yourself writing some programs to make yourself more easy with load and store operations.
Here is the list of programs you can try out:

1. Swap two numbers stored in RAM
   
2. Find Greatest of 5 numbers
   
3. Copy memory block from RAM to RAM
   
4. Sorting of 10 numbers
   
5. Clear SRAM area from 0x60 to RAMEND

AVR UART Programming

Learn to program AVR in C as well as assembly for serial Programming or UART programming.

ADC0804 interfacing tutorial

Interface an 8-bit ADC (ADC0804) with AVR microcontroller.

Keypad Tutorial
Learn to interface a 4x4 matrix keypad with AVR microcontroller.