RetroShield emulates classic 8-bit computers with an Arduino Mega. On the daughter card (shield), there is a real 8-bit microprocessor like the 6502, Z80, or 6809. The Arduino Mega emulates the RAM, ROM, and I/O devices. It also provides a terminal connection back to the host PC. With this combination, it is possible to emulate vintage computers such as the Apple I or Commodore 64.
The RetroShield is developed by Erturk Kocalar of 8 Bit Force and sells for $18 (unassembled.) The kit includes a daughter card, a socket, header pins, and an LED along with a 6502, Z80, or 6809. Kocalar told me he is sourcing vintage chips from the various sources and then joked he will not expose them in fear of the supply drying up! For the 6502, he does have modifications for a modern W65C02 replacement when the NOS (new-old-stock) runs out.
You need an Arduino Mega because the emulation is RAM intensive. Kocalar says he is working on support for an external SPI RAM. When entering a very long basic program on the Apple I, my RAM ran out. I am definitely looking forward to seeing the added support.
Do not expect to load the C64 core and run Jumpman with the RetroShield. Emulated clock speeds are well below the original ~1 MHz. Instead, think of this platform as “wire-wrapping in software.” The above screenshot is the Apple I emulation with a small assembly language program to print a modified hello world. This kind of tinkering seems inline with the spirit of RetroShield.
Related, 8 Bit Force joined up with Eric at VCFWest 2019. Kocalar created the MOnSter 6502, which is an enormous re-creation of the 6502 processor using discrete transistors. The photo above shows the MOnSter 6502 connected to the RetroShield6502 running code.
Find more information on the RetroShield over on 8 Bit Force’s Tindie store.
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Author: James Lewis