ABOUT AVR

AVR Microcontroller

History of AVR

                          AVR was developed in the year 1996 by Atmel Corporation. The architecture of AVR was developed by Alf-EgilBogen and VegardWollan. AVR derives its name from its developers and stands for Alf-EgilBogen VegardWollan RISC microcontroller, also known as  Advanced Virtual RISC. The AT90S8515 was the first microcontroller which was based on  AVR architecture however the first microcontroller to hit the commercial market was AT90S1200 in the year 1997.

AVR microcontrollers are available in three categories:

1.      TinyAVR – Less memory, small size, suitable only for simpler applications

2.      MegaAVR – These are the most popular ones having good amount of memory (upto 256 KB), higher number of inbuilt peripherals and suitable for moderate to complex applications.

3.      XmegaAVR – Used commercially for complex applications, which require large program memory and high speed.

The following table compares the above mentioned AVR series of microcontrollers:

Series name	Pins	Flash Memory	Special Feature
Tiny AVR	6-32	0.5-8 KB	Small in size
Mega AVR	28-100	4-256KB	Extended peripherals
Xmega AVR	44-100	16-384KB	DMA , Event System included

                  In our journey with the AVR we will be working on Atmega16 microcontroller, which is a 40-pin IC and belongs to the megaAVR category of AVR family. Some of the features of Atmega16 are:

•            16KB of Flash memory
•            1KB of SRAM
•            512 Bytes of EEPROM
•            Available in 40-Pin DIP
•            8-Channel 10-bit ADC
•            Two 8-bit Timers/Counters
•            One 16-bit Timer/Counter
•            4 PWM Channels
•            In System Programmer (ISP)
•            Serial USART
•            SPI Interface
•            Digital to Analog Comparator.

There are two flavors for Atmega16 microcontroller:

1.      Atmega16:- Operating frequency range is 0 – 16 MHz.

2.      Atmega16L:- Operating frequency range is 0 – 8 MHz.

                      If we are using a crystal of 8 MHz = 8 x 10⁶ Hertz = 8 Million cycles, then AVR can execute 8 million instructions.

Naming Convention.

                    The AT refers to Atmel the manufacturer, Mega means that the microcontroller belong to MegaAVR category, 16 signifies the memory of the controller, which is 16KB.

        

Memory: Atmega16 consist of three different memory sections:

1.      Flash EEPROM: Flash EEPROM or simple flash memory is used to store the program   dumped or burnt by the user on to the microcontroller. It can be easily erased electrically as a single unit. Flash memory is non-volatile i.e., it retains the program even if the power is cut-off. Atmega16 is available with 16KB of in system programmable Flash EEPROM.

2.        Byte Addressable EEPROM: This is also a nonvolatile memory used to store data like values of certain variables. Atmega16 has 512 bytes of EEPROM, this memory can be useful for storing the lock code if we are designing an application like electronic door lock.

3.        SRAM: Static Random Access Memory, this is the volatile memory of microcontroller i.e., data is lost as soon as power is turned off. Atmega16 is equipped with 1KB of internal SRAM. A small portion of SRAM is set aside for general purpose registers used by CPU and some for the peripheral subsystems of the microcontroller.

·           ISP: AVR family of controllers have In System Programmable Flash Memory which can be programmed without removing the IC from the circuit, ISP allows to reprogram the controller while it is in the application circuit.

·          SPI: Serial Peripheral Interface, SPI port is used for serial communication between two devices on a common clock source. The data transmission rate of SPI is more than that of USART.

·           TWI: Two Wire Interface (TWI) can be used to set up a network of devices, many devices can be connected over TWI interface forming a network, the devices can simultaneously transmit and receive and have their own unique address.

·           DAC: Atmega16 is also equipped with a Digital to Analog Converter (DAC) interface which can be used for reverse action performed by ADC. DAC can be used when there is a need of converting a digital signal to analog signal.