Just 4 Fun's V20-MBC Is an Expandable CP/M Single-Board Computer Built Around NEC's V20HL CPU
Designed around the CPU that NEC reverse-engineered as a competitor to Intel's 8088, the V20-MBC is created to be easy to build.
YouTuber and electronics engineer "Just 4 Fun" has created a new vintage-inspired single-board computer based on the V20HL static CMOS processor — and with up to 1MB of RAM, an optional 16-pin general-purpose input/output (GPIO) port, and I2C expansion, plus two flavors of CP/M.
"The V20-MBC is an easy to build V20HL (full static CMOS version) or 80C88 CPU SBC (Single Board Computer)," Fun explains in the project's write-up. "It follows the same 'concept' of the Z80-MBC2, with a[n] SD as 'disk emulator' and up to 1024kB RAM. It has an optional on-board 16 GPIO expander, and uses common cheap add-on modules for the SD and the RTC options. It has an 'Arduino heart' using an ATmega32A as EEPROM and 'universal' I/O emulator (so a 'legacy' EPROM programmer is not needed) programmed with Arduino IDE."
The board is built around the NEC V20HL, a full static CMOS version of NEC's V20 — a chip made by NEC by reverse-engineering Intel's at-the-time shiny new 8088 and fitting it with an instruction set equivalent to the Intel 80186. As a pin-compatible part, it's also possible to replace it with an Intel original 80C88 - the CMOS variant of the 8088 — or any other pin-compatible 8088-alike.
As well as the CPU and supporting microcontroller, the board design includes 1MB of RAM which can be configured as 128kB, 512kB, or 1MB depending on requirement, optional real-time clock and microSD modules, an I2C expansion header, serial port, user-programmable switch and LED, and the choice of 4MHz and 8MHz operation modes.
"The software running into the ATmega32A is the IOS (Input Output Subsystem) written using the Arduino IDE environment," Fun notes. "The IOS allows to interface the ATmega32A directly with the CPU system bus, emulating the needed I/O chips during the I/O read, I/O write and IRQ acknowledge CPU bus cycles."
An SD card image contains a range of utilities, including a tool for loading 8088- or 8080-compatible Intel hex files from the serial port, and support for CP/M-80, CP/M-86, and a smart emulation mode for running CP/M-80 software in CP/M-86.
Full project details can be found on Fun's Hackaday.io page; PCBs, meanwhile, can be ordered from PCBWay where the Gerber files are also available.