Karl’s Serial and Storage Module #61c

This module (karlab #61c) has been designed for RC2014 by Karl Albert Brokstad. It provides a serial port and mass storage using a Compact Flash card.

It pairs well with SC108 Z80 Processor module to make a two module CP/M system.

Documentation and Suppliers

DocumentationDeveloper’s website
PCB design filesEasyEDA: karlab #61c
PCB design filesZ80.no: karlab #61c
PCB (to purchase)Tindie: Rotten Snow #61c
Kit (to purchase)Tindie: Rotten Snow #61c


This module provides the following features:

  • Serial port for communications
  • Compact Flash for storage
  • Local clock source independent of the bus clock
  • Useful range of configuration jumpers
  • Tight address decoding for Compact Flash
  • Reasonably tight decoding for serial port
  • Compatible with standard RC2014 software
  • Compatible with RomWBW
  • Appears compatible with Z80 clocked at 20 MHz

The PCB is nicely laid out with an outline similar to most RC2014 moldules. The bus connector is the full 40 pin length so the module is slightly longer than most. However, being 40 pins long means it fully matches the 40 pin sockets on RC2014 backplanes.

The module houses a 68B50 based asynchronous serial port with a 5 volt FTDI style serial header. It also includes a Compact Flash interface with the Compact Flash card fitted on a readily available adapter board. This avoids the need to solder the fine surface mount Compact Flash socket.

The Compact Flash adapter (the green board above) can be soldered directly to the edge of the module (as shown) or can be fitted via a socket.

By providing both a serial port and a Compact Flash interface on the same module, a backplane slot is saved. This allows a CP/M system to be created with just 2 modules (SC108 plus #61c) and a small backplane (SC116).

The result is a neat little CP/M system.

Of course, you don’t just have to use this module to create a minimal CP/M system; It can be use as part of a much bigger system.

The only real disadvantage of this design is that the Compact Flash adapter sticks out a long way.

Homebrew 8-bit retro computing