Avr introduction

Anant Shrivatsava EI – 7 th SEM

INTRODUCTION

AVR or Atmel AVR are RISC based family of microcontroller produced by Atmel Corporations

The acronym AVR has been reported to stand for Advanced Virtual RISC, but it has also been rumored to stand for the initials chip's designers: Alf and Vegard [RISC]. Atmel says that the name AVR is not an acronym and does not stand for anything in particular.

The original AVR MCU was developed at a local ASIC house in Trondheim Norway, where the two founders of Atmel Norway were working as students. It was known as a uRISC (MicroRISC). The internal architecture was further developed by Alf and Vergard.

The AVR is a Harvard architecture machine with programs and data stored separately.

AVRs are generally classified into three broad groups:

tinyAVRs

1-8 kB program memory

8-20-pin package

Limited peripheral set

megaAVRs

4-256 kB program memory

28-100-pin package

Extended instruction set and peripheral set

Application specific AVRs

megaAVRs with special features not found on the other members of the AVR family, such as LCD controller, USB controller, advanced PWM etc.

Device Architecture Data RAM Flash, EEPROM, and SRAM are all integrated onto a single chip, removing the need for external memory (though still available on some devices). Program Memory Program instructions are stored in non-volatile Flash memory. Although they are 8-bit MCUs, each instruction takes 16 bits with an 8-bit opcode followed by 8 bits of data or an address to be modified by the previous instruction. So the flash memory is actually addressed in a 16-bit fashion. Internal Data Memory The data address space consists of the register file, I/O registers, and SRAM. The AVRs have 32 single-byte registers and are classified as 8-bit RISC devices.

Internal Registers The working registers are mapped in as the first 32 memory addresses (000016-001F16) followed by the 64 I/O registers (002016-005F16). Actual SRAM starts after the register sections (address 006016). EEPROM Some AVR microcontrollers have internal Electrically Erasable Programmable Read Only Memory (EEPROM) for semi-permanent data storage. Like Flash memory, EEPROM can maintain its contents when electrical power is removed.Since the number of writes to EEPROM is not unlimited - Atmel specifies 100,000 write cycles in their datasheets. More on Device Architecture

Program Execution Atmel's AVRs have a single level pipeline design. This means the next machine instruction is fetched as the current one is executing. Most instructions take just one or two clock cycles, making AVRs relatively fast among the eight-bit microcontrollers. The AVR family of processors were designed with the efficient execution of compiled C code in mind and has several built-in pointers for the task. MCU Speed The AVR line can normally support clock speeds from 0-16 MHz, with some devices reaching 20 MHz. Lower powered operation usually requires a reduced clock speed. All AVRs feature an on-chip oscillator. Since many operations on the AVR are single cycle, the AVR can achieve up to 1MIPS per MHz.