AVR Microcontrollers

AVR is a microcontroller belonging to the family of Reduced Instruction Set Computer(RISC). In RISC architecture the instruction set of the computer are not only fewer in number but also simpler and faster in in operation. AVR was developed in year 1996 by Atmel corporation. The architecture of AVR was developed by Alf-Egil Bogen and Regards Swollen. AVR derives from its developers and stands for Alf-Egil Bogen Vegard Wollen RISC microcontroller, also known as Advanced Virtual RISC machine. The AT90S8515 was 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 as shown below;

Series Name	Pins	Flash Memory	Special Features
Tiny AVR	6-32	0.5-8Kb	Small in size
Mega AVR	28-100	4-256Kb	Extended peripherals
XmegaAVR AVR	44-100	16-384Kb	DMA,Event system included

TinyAVR:-

Less memory, small size, suitable only for small applications.

MegaAVR:-

These are most popular ones having good amount of memory(256Kb), higher number of inbuilt peripherals and suitable for moderate to complex applications.

XmegaAVR:-

Used commercially for complex applications which require large program memory and high speed.

AVR microcontrollers are fast:AVR microcontroller executes most of the instructions in single execution cycle. AVRs are about 4 times faster than PICs, they consume less power and can be operated in different power saving modes. Let's do the comparison between the most commonly used families of microcontrollers;

Parameters	8051	PIC	AVR
Speed	Slow	Moderate	Fast
Memory	Small	Large	Large
Architecture	CISC	RISC	RISC
ADC	Absent	Inbuilt	Inbuilt
Timers	Inbuilt	Inbuilt	Inbuilt
PWM Channels	Absent	Inbuilt	Inbuilt

Features
• High-performance, Low-power Atmel®AVR® 8-bit Microcontroller
• Advanced RISC Architecture
– 131 Powerful Instructions – Most Single-clock Cycle Execution
– 32 × 8 General Purpose Working Registers
– Fully Static Operation
– Up to 16 MIPS Throughput at 16MHz
– On-chip 2-cycle Multiplier
• High Endurance Non-volatile Memory segments
– 32Kbytes of In-System Self-programmable Flash program memory
– 1024Bytes EEPROM
– 2Kbytes Internal SRAM
– Write/Erase Cycles: 10,000 Flash/100,000 EEPROM
– Data retention: 20 years at 85°C/100 years at 25°C(1)
– Optional Boot Code Section with Independent Lock Bits
In-System Programming by On-chip Boot Program
True Read-While-Write Operation
– Programming Lock for Software Security
• JTAG (IEEE std. 1149.1 Compliant) Interface
– Boundary-scan Capabilities According to the JTAG Standard
– Extensive On-chip Debug Support
– Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
• Peripheral Features
– Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes
– One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture
Mode
– Real Time Counter with Separate Oscillator
– Four PWM Channels
– 8-channel, 10-bit ADC
8 Single-ended Channels
7 Differential Channels in TQFP Package Only
2 Differential Channels with Programmable Gain at 1x, 10x, or 200x
– Byte-oriented Two-wire Serial Interface
– Programmable Serial USART
– Master/Slave SPI Serial Interface
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
• Special Microcontroller Features
– Power-on Reset and Programmable Brown-out Detection
– Internal Calibrated RC Oscillator
– External and Internal Interrupt Sources
– Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby
and Extended Standby
• I/O and Packages
– 32 Programmable I/O Lines
– 40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF
• Operating Voltages
– 2.7V - 5.5V for ATmega32L
– 4.5V - 5.5V for ATmega32
• Speed Grades
– 0 - 8MHz for ATmega32L
– 0 - 16MHz for ATmega32
• Power Consumption at 1MHz, 3V, 25°C
– Active: 1.1mA
– Idle Mode: 0.35mA
– Power-down Mode: < 1µA