Z80 Computer SC114 with CP/M 2.2

This is an SC114 fitted with an add-on board to enable loading and running the CP/M 2.2 operating system. The add-on board I use is known as “the missing module” designed by Karl A. Brokstad in Norway. The Serial and Storage module #61 (the official name of the board) contains an MC68B50 serial port running at 115200 baud, and a compact flash card interface.

For less than $100 you get a system with the capacity of systems costing $1000+ in the 80s…

SC114 with Serial+Storage Module
SC114 with Serial+Storage Module

The compact flash card is used as “disk drive” for CP/M, and the Small Computer Monitor in the SC114 contains a loader in ROM, which can load CP/M from the compact flash card. The module comes with a 64MB compact flash card, formatted and pre-installed with CP/M and several programming tools and utilities. If you want to prepare a compact flash card yourself, please follow the instructions in the SC114 documentation.

You can also download my “vanilla package” of CP/M 2.2 tested on the SC114 (expect for MOVCPM.COM which does NOT work unless tailored for the specific system). See page Digital Research CP/M 2.2 for a short description of the files. Use either DOWNLOAD.COM or DEPKG.COM to unpack the files (follow the SC114 documentation linked above if you do not have one of these files on your system already).

I also added a Wifi module to the SC114 system.

Troubleshooting first built of storage module (version 61f)

When I first installed the board (version 61f), I had problems getting the compact flash adapter to work reliably. With help from the competent people in the google group retro-comp, I was adviced to install a filter on the IORD pin using a 100pf capacitor and a 100R ohm resistor. After installing this patch, the board is now 100% stable.

However, Karl has made a new version of the module correcting this problem (version 61g in the picture above), so if you consider buying one I recommend checking out Karl’s excellent website for current information. I have built and tested the new version, and I can confirm it is running reliably in my SC114 system.

But if you happen to have the older version and experience problems you may try this patch.

Patch installed in module version 61f

I got the diagram below from Karl, illustrating the patch. Actually, I only installed the patch on !RD which apparently was what I needed to correct the problem in my SC114 system.

Patch diagram for version 61f