[Scott Baker] wanted to take on a new retrocomputing project. He decided to build an RC2104. Lucky for us, he documented everything along the way. In addition to the main board, [Scott] built bus monitoring and debugging tools, a front panel, a real time clock, an analog to digital converter, and a speech synthesizer.
You can follow along in the 8-part post that includes videos. He started with the basic kit:
- CPU – The Z80
- ROM – 27C512 64 KB ROM, selectable in 8KB banks
- RAM – 62256 32 KB RAM
- Clock – 7.3728 Mhz crystal that drives a 74HC04 hex inverter (for the CPU and the UART)
- Serial I/O – MC68B50 UART
In addition, he picked up a digital I/O board.
The custom boards cover a wide range of functions:
- Real Time Clock (RTC) and digital output
- Bus Supervisor – A Raspberry Pi to control the bus for development
- Bus Monitor – Display address and data busses
- Front Panel – Switches and LEDs as an I/O device
- Single Stepper / Slow Stepper – Slow down execution (without it, the bus monitor isn’t very useful)
- Speech Synthesizer – A 1980s-style voice using a SP0256A-AL2
This is a great exposition of building and designing a vintage Z-80 computer. There’s a good discussion of the interfacing and bus operation. This system would have been way beyond state of the art in 1979.
We’ve talked about the RC2014 before. We’ve even covered projects using the venerable SPO256 speech synthesizer.