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Very Slow Progress on the SWTPC Clone

Since the arrival of the CPU board and motherboard prototypes, I’ve been busy all day at my primary customer’s site, filling orders for KIM boards, family, and Boy Scout activities.

There is a mostly populated CPU board that’s fetching data from the EPROM but not working properly and I just haven’t had enough time to sit down with the logic analyzer to find what’s going on.  The first board needed three cuts and two jumpers to get this far and it appears address lines are properly buffered, correctly decoded, and getting to the EPROM, so the next step is to see what’s coming out when the reset vector is fetched.

A single motherboard has enough on it so the CPU can plug in, get power, and the reset button works.

I have commitments to Boy Scouts all weekend but will start to have free time again next week to get this project working.

The 64K RAM board prototypes should arrive any day now, so I’ll build one up and send to a beta user for testing.


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6800 Motherboard and CPU Boards Arrived!

These are just a couple quick shots of the unpopulated boards.

6800 CPU:



One motherboard has just enough assembled so that the partially populated CPU board can plug in to get 8 volts.

One CPU is slowly coming up.  I was at a customer site all day so didn’t get to work on these until evening, and have the power supply, baud rate generator and main CPU clocks tested.  Tomorrow I should have time to get the signal buffering, address decoding, and maybe the EPROM working.


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MP-S Rev 2 Boards are built and working

In the test jig, running just fine…


They can be built with the DB-9 facing up or to the side, or both.  The Molex connector on top is compatible with the original MP-S connector.

Once the beta tester gives a thumbs-up, I’ll order production versions and put the boards on the market.

BTW, the board it is plugged into is a prototyping board.  I don’t have a real SWTPC system yet to test with, so I ended up building a small 6800 system with 4K EPROM, 8K RAM, a baud rate generator and very basic decode logic.  At first I used jumper wires to connect the MP-S boards for testing but that as error prone, so I built a board that plugs into the wireless breadboard on one side and provides an SS-30 connector.