AVR microcontrollers
They are especially common in hobbyist and educational embedded applications, popularized by their inclusion in many of the Arduino line of open hardware development boards.
The AVR architecture was conceived by two students at the Norwegian Institute of Technology (NTH),[1] Alf-Egil Bogen[2] and Vegard Wollan.
[7] Among the first of the AVR line was the AT90S8515, which in a 40-pin DIP package has the same pinout as an 8051 microcontroller, including the external multiplexed address and data bus.
[8] The Arduino platform, developed for simple electronics projects, was released in 2005 and featured ATmega8 AVR microcontrollers.
Flash, EEPROM, and SRAM are all integrated onto a single chip, removing the need for external memory in most applications.
There is no provision for off-chip program memory; all code executed by the AVR core must reside in the on-chip flash.
However, some devices in the SecureAVR (AT90SC) family[11] use a special EEPROM mapping to the data or program memory, depending on the configuration.
Most instructions take just one or two clock cycles, making AVRs relatively fast among eight-bit microcontrollers.
The AVR processors were designed with the efficient execution of compiled C code in mind and have several built-in pointers for the task.
All recent (Tiny, Mega, and Xmega, but not 90S) AVRs feature an on-chip oscillator, removing the need for external clocks or resonator circuitry.
In order to avoid the chip accidentally entering such mode, it is advised to connect a pull-up resistor between the RESET pin and the positive power supply.
The PDI supports high-speed programming of all non-volatile memory (NVM) spaces; flash, EEPROM, fuses, lock-bits and the User Signature Row.
It is also possible to use an Arduino thanks to jtag2updi,[19] or a standard USB-UART adapter with the TX and RX pin shorted by a 1 kΩ resistor and the pymcuprog utility provided by Microchip.
High-voltage parallel programming (HVPP) is considered the "final resort" and may be the only way to correct bad fuse settings on an AVR chip.
The Joint Test Action Group (JTAG) feature provides access to on-chip debugging functionality while the chip is running in the target system.
[27] JTAG allows accessing internal memory and registers, setting breakpoints on code, and single-stepping execution to observe system behaviour.
The STK500 starter kit and development system features ISP and high voltage programming (HVP) for all AVR devices, either directly or through extension boards.
The board has a 4 MHz clock source, 8 light-emitting diode (LED)s, 8 input buttons, an RS-232 port, a socket for a 32 KB SRAM and numerous general I/O.
The Atmel ICE is the currently supported inexpensive tool to program and debug all AVR devices (unlike the AVRISP/AVRISP mkII, Dragon, etc.
The Atmel-ICE supports a limited implementation of the Data Gateway Interface (DGI) when debugging and programming features are not in use.
As the AVRISP mkII lacks driver/buffer ICs,[36] it can have trouble programming target boards with multiple loads on its SPI lines.
Alternatively, the AVRISP mkII can still be used if low-value (~150 ohm) load-limiting resistors can be placed on the SPI lines before each peripheral device.
[38] The Dragon has a small prototype area which can accommodate an 8, 28, or 40-pin AVR, including connections to power and programming pins.
The board includes the LCD screen, joystick, speaker, serial port, real time clock (RTC), flash memory chip, and both temperature and voltage sensors.
This small board, about half the size of a business card, is priced at slightly more than an AVR Butterfly.
It includes an AT90USB1287 with USB On-The-Go (OTG) support, 16 MB of DataFlash, LEDs, a small joystick, and a temperature sensor.
Atmel ships proprietary (source code included but distribution restricted) example programs and a USB protocol stack with the device.
The kit includes two AVR Raven boards, each with a 2.4 GHz transceiver supporting IEEE 802.15.4 (and a freely licensed Zigbee stack).
Raven peripherals resemble the Butterfly: piezo speaker, DataFlash (bigger), external EEPROM, sensors, 32 kHz crystal for RTC, and so on.
Microcontrollers using the ATmega architecture are being manufactured by NIIET in Voronezh, Russia, as part of the 1887 series of integrated circuits.
