The Retro-µC: Putting the Open into Retro Computing CPUs

Alasdair Allan
3 min readAug 28, 2018

We’ve seen a lot of retro computing projects over the last year or two. Perhaps it’s because those of us that grew up before the arrival of home computing have reached a certain age and are returning to the classics, but in recent months there seems to be more and more retro computing projects crossing over my desk. I can’t open my email without someone pitching me an FPGA-based retro computing project.

But the Retro-µC isn’t one of those. Now raising on Crowd Supply, the Retro-µC is an open source silicon ASIC that houses the RTL for three retro computing cores; the Zilog Z80, the MOS Technology 6502, and the Motorola 68000.

The “Retrino,” an Arduino MEGA form factor board powered by the Retro-µC chip. (📷: Staf Verhaegen)

The first project under the “Chips4makers” umbrella, Retro-µC is being developed in the open, with the intention that all the code, chip, and PCB designs will be released as open source.

The Retro-µC chip will be released in a QFP package and will have 4 kB of on-chip RAM, and 72×5V digital GPIO pins, along with a JTAG interface for programming. It will be optionally bootable from external I2C flash memory, and potentially may ship with on-chip UART, I2C, or PWM controllers.

In addition to shipping the chip on its own, several boards are going to be made available, including the ‘Retrino,’ an Arduino MEGA form factor board powered by the Retro-µC chip.

“The Retrino is a board that integrates the Retro-µC with an Arduino compatible I/O layout. The 72 5 V I/O pins are accessed via headers that are compatible with the Arduino Mega. These I/Os can then be used for projects using custom wiring or existing Arduino Uno and Mega shields. A companion micro-controller on the board allows you to program the board through USB and store the program in its on-chip NVM. Afterwards, the board can be used as a standalone that only needs 5 V power over the USB connector.”

The ‘Retrino’ isn’t the first MEGA form factor board we’ve seen recently. But, despite the Arduino old school form factor, you shouldn’t expect an Arduino-like development environment for the new chip, as it can be programmed “…through assembly language or via an [already] available C compiler that exists for the three cores.”

While the chip design with the Z80, MOS6502 and the Motorola 68000 cores are now finished and have been tested in an FPGA on the XLR8 board. Support for peripherals like UART, PWM, and I2C have still to be integrated.

Presentation by Chips4Makers at ORConf 2017. (📹: FOSSi Foundation)

You can find out more about the project on its project page, and associated GitLab repos. The Retro-µC is currently on Crowd Supply. You can get your hands on a Retro-µC chip in a QFP package for $42, or a five pack of chips for $189, with free shipping inside the United States, and an extra $8 for world wide shipping. While if you’re interested in the ‘Retrino,’ a Retro-µC based board with Arduino MEGA footprint and compatible I/O, it is also now available costing $89.