View Full Version : A New Single Board Z80 based S100 bus board is now available.

October 17th, 2015, 10:56 AM
:pI’m glad to report that the 2nd prototype version of our Z80 based S100 Bus SBC seems to be working fine. This S100 board has a Z80A on board with 128k of RAM, and 8K (or 4K) of EEPROM. It is geared for first time S100 bus users to get a basic system up and running. The board has a USB socket to communicate with a laptop/PC as a serial I/O terminal. The board has an IDE Port to use with a CF-CARD Adaptor to run an operating system such as CPM. Because the lower 32K of RAM can be switched with another 32K of RAM the board should work well with CPM3. There are is an onboard IOBYTE port to redirect data I/O to (for example) our S100 bus Console I/O board. There are numerous jumpers to reconfigure the board. Things like inactivating the onboard RAM, ROM, IDE port etc. to gradually add other S100 boards to your system. The “BASE_PORT” for a range of the boards’ eight I/O ports is configurable (0-255). There is a Power On Jump (POJ) circuit to the onboard EEPROM at any 4K boundary. The Z80/S100 bus interface circuit seems to work with all (old) S100 bus RAM boards I have (~10), even DRAM boards like the IMS 64K board as well as all I/O boards I have. This is at 4 or 5MHz (no wait states).

While the board will act as a master/slave S100 board it’s not really intended to function is a complex multiprocessor configuration. For example for debugging you cannot “see” beyond 64K of RAM in the bus. However you can actually transfer control over to our slave 8086 CPU board.


I have written a basic Z80 monitor with the usual Zapple/Master commands. There is an XModem command to download files from your PC (via the USB port) and run in the boards RAM (at any defined location). There are commands to read, display and write multiple sectors to/from the onboard IDE/CD Card. Because of time constraints, I have NOT written a CPM/CPM3 BIOS etc. to run the operating system from the board. Everything you need is there; hopefully somebody can do this and have it available for all. See the S100Computers Software page to get started. There is a basic BOM list there also.
A description of the board can be seen here:-

I will be doing a batch of (gold plated) production boards soon. If you would like one or more boards please let me know. To do so please go to the bottom of the above web site page and sign on to the Google Groups forum to handle this.