Progress – Finally!

Friday, July 11th, 2014

Production versions of the Serial board and 64K boards have been ordered and should arrive in about two weeks.

Today I had the whole system up and running… my new motherboard, the 6800 CPU board and the serial board.  It doesn’t do much yet, as there are still some glitches that need to be ironed out, but at least things are working.  Neither the CPU nor motherboard are good-enough to sell, so a second pass will be needed.  The motherboard is very close to correct but needs to be a lot thicker to handle the mechanical stresses of inserting and removing boards with those Molex connectors.  Also missed buffering of two signals but that was easy to get around for debugging.

My time for work is going fast; near the end of the month I’m heading out to the Philmont Scout Reservation in New Mexico with my son and a small group of Scouts and adults.  This is a two week backpacking trek, so the soldering iron, spare parts, computers, and prototype PC boards will be left at the bench back in New Jersey.  I am really looking forward to this!



6800 CPU Board is Alive!

Friday, July 4th, 2014

That was a lot of debugging for what turned out to be a simple problem… the 2764 EPROM with test code wasn’t working!  I was debugging all the logic around it, finally replacing it last and then the board came to life!  Of course that meant spending time to undo all the cuts/jumpers that weren’t really needed.

This is prototype #1 in prototype motherboard #1 with some logic analyzer probes.  The test code in EPROM simply does reads/writes to all the regions of memory to check that the block decoding is working:


There is a lot of debugging to do still.  Next is to make sure the buffer logic for interfacing to the bus works properly.  Once that’s operational, then I need to move back to the motherboard and get that built up/tested.  Right now it’s doing little more than providing a reset button (on the left) and power.

Right now, I’m regretting not putting a serial port on the CPU board.  It’s almost a single board 6800 computer, but needs the motherboard and serial board for I/O.

Time for some fireworks :-)


SS-50 (SWTPC) 64K RAM Board Working!

Wednesday, July 2nd, 2014

The beta user said that the board is working in his system!


The board uses a few parts not available in the 1970s, so while it’s not vintage, it’s a nice addition if more memory is needed.  It offers the following features:

  • 64K
  • Each 4K segment can be individually turned on/off
  • Only three ICs, plus the voltage regulator and a few analog parts.
  • Very low power draw
  • Final list price will be must lower than any SS-50 RAM board was in the 1970s!

This is still an engineering prototype.  Once the beta user has beaten it up more and finds no problems, I’ll order production quality PC boards and go into production.

If you’re interested in a board before then, just email me: and let’s talk.