I also sell Arduino boards like the Arduino Nano, Arduino Uno and several AVR based chips in mu webshop and although they are strictly not retro, they are used in a lot of Retro replicas, retroshields and chip testers. I build a lot of chip testers based on an Arduino board and I also have some PCB’s for these in my webshop. On this page I will tell you a little more about these AVR chips. AVR is a family of microcontrollers developed since 1996 by Atmel and acquired by Microchip Technology in 2016. The AVR chips are modified Harvard architecture 8-bit RISC single-chip microcontrollers and they were one of the first microcontroller families to use on-chip flash memory for program storage.
The AVR architecture was conceived by two students at the Norwegian Institute of Technology (NTH) named Alf-Egil Bogen and Vegard Wollan. Atmel says that the name AVR is not an acronym but it is commonly accepted that AVR stands for Alf and Vegard’s RISC processor. One of the first chips of the AVR line was the AT90S8515 and the processors got a big boost when the Arduino platform was released in 2005 and featured the ATmega8 AVR microcontrollers.
The Arduino based boards (but also the individual chips using SPI) can be easily programmed in assembler and the ‘C’ and ‘C++’ language and there are a lot of ready to use libraries for different devices and communication protocols.. The fact that (most of ) these chips use 5V power supply makes them also interesting to use in combination with old hardware and old chips. They are often used as a boot device and serial controller in several designs like the Z80 MBC and the Apple1 replica.
The ATMega32 is a high-performance, low-power Microchip 8-bit AVR® RISC-based microcontroller that combines 32 KB ISP flash memory with 1 KB EEPROM, 2 KB SRAM, 54/69 general purpose I/O lines, 32 general purpose working registers, three flexible timer/counters with compare modes, internal and external interrupts, serial programmable USART, an 8-channel 10-bit A/D converter, programmable watchdog timer with internal oscillator, SPI serial port, and five software selectable power saving modes. The device operates between 1.8-5.5 volts. This makes it suitable as external rom for boot and serial and I/O device for retro microprocessors like the Z80. The ATMega32 is used in a lot of MBC (Minimal Computer Board) designs like the Z80 MBC.
The Arduino Mega is a big Arduino board based on the ATmega2560. It has 256 KB of Flash Memory ( 8 KB used by bootloader), 8 KB Sram and 4 KB Eeprom, 54 digital input/output pins, 16 analog inputs, 4 UARTs (hardware serial ports) and a 16 MHz crystal oscillator. This makes it perfect to emulate Rom / Ram and I/O for a lot of old 8bit microprocessors. There are a lot of so called Retroshields for a wide verity of 8 bit processors like the Z80, the 6502, the 1802, the 2605 and 68xx processors. Sometimes even a small system using basic or emulation of an old computer is available in open source.
The Ardiono Uno and the Arduino Nano are often used as basic boards for chip testers, ISP programmers and f.i. as serial interface on a Retro computer where these boards replace a lot of glue logic. On the Apple1 replica the Arduino Nano replaces the terminal interface emulating the keyboard and the CRT interface. I also sell a dram tester based on Arduino Uno or Arduino Nano boards.
In retro designs the AVR chips are very handy to replace a lot of glue logic and I/O devices, because the AVR chips and boards support SPI they can easily interface to cheap SD card disk drives and realtime clock boards. So even if these chips are not retro themselves, the are often used in combination with Retro computers.
Have fun, regards, Hein Pragt.
