When I first started making SS-50/SS-30 boards, the very first design was a serial board. Since I had no SWTPC machine to test in, I reached out to Bill Degnan of Kennett Classic asking if he could test it. Once that was known working, the next things I needed for a real SS-50 machine were a CPU board and a motherboard. The motherboard has been redesigned a few times and the current design, revision 5, is quite solid.
However, the original 6800 CPU board never had a major update in years, and still had only 16K of RAM. Back when I took the original SWTPC design and updated it I just wasn’t sure exactly what options would be desirable, how much RAM/EEPROM to have on it, etc. It required an external memory board to do anything useful, and it really looks like nobody had done much with the spare EPROM sockets on the original SWTPC CPU board. So, I started a re-design a couple years ago but never quite finished it until about a month ago.
The result:
Basic features are similar to the original 6800 CPU but a with few changes:
- 64K RAM on board! No need to have an external RAM board.
- Baud rate generator now uses more common parts; does not use the MC14411 any more. Supports 1200, 2400, 4800 and 9600 baud.
- Power LED. No big deal, but it’s nice to see power is on before pulling out a board!
The shopping page for the board still shows the old revision; need to update that. The price will eventually go from $125 to $130 but the current price ($125) will be in effective through at least September 1st.
The weird version number 3A is because I suspected a few spins would be required to work out bugs, but the first version “A” worked so that’s the current version number.
65C02 CPU Board
I had an earlier version of this board but never offered it for sale, but a couple people have asked for it and asked for a specific change to give it more EEPROM space, so this will be for sale after I return from the hospital:
Basic features:
- Uses a genuine WDC65C02, not some unknown Chinese chip, running at 2 MHz.
- Lower 32K is all RAM (0000-7FFF).
- Upper 32K can enable RAM in 4K chunks. The intent is that it will have RAM from 0000-DFFF, I/O from E000-E1FF and then EPROM from E200-FFFF.
- A switch allows extended EEPROM to overlay unused address space in the I/O region, so E200-FFFF is all available for code.
- Includes CTMON65 (https://github.com/CorshamTech/CTMon65) but there is at least one other person writing an alternative monitor.
- Has a single-step circuit which operates exactly like the KIM-1 and KIM Clone. If an instruction is fetched that is not in the EEPROM, it generates an NMI. Turned on/off via a DIP switch.
- The EEPROM socket supports a 32K device and any 8K segment can be selected via jumpers. We include an 8K device.
- Power-on reset. Okay, so that’s not a vintage part, but is really nice not having to press RESET at power-up.
Please note that there was never any universal DOS for 6502 machines, as every manufacturer wrote their own, so there is no option to boot/load any DOS. CTMON65 does allow saving/loading Intel hex files but there is no option to boot. Anyone who buys this board needs to realize this is kind of an experimental board for software development. Perhaps someone would like to port DOS/65?
Pricing will be the same as the 6800 CPU board: $25 for a bare board, $130 for an assembled/testing board.
Parts Shortage
For the past few weeks I’ve had a parts shortage again. A large order for MC14411s hasn’t arrived so I got a small number delivered quickly but rather expensively. My main supplier of the Molex female connectors ran out of stock and won’t ship the rest of my order until July, so I ordered some from another source (at about three times the cost). I also ran out of 6809 boards and motherboards; they were ordered a few weeks ago but the manufacturer is still backed up because of COVID-19 so they should arrive in about a week. I have been more focused on short-term medical issues and the business wasn’t getting the attention that it needs.
