Lots of Stuff in Progress

Friday, January 16th, 2015

The new and improved SS-50 motherboard engineering samples arrived and have tested out nicely with the 6800 CPU.  I’ve been using one of them non-stop for use in the lab and they work great.  A few features:

  • Base address for the I/O slots can be set to either 8000 (6800) or E000 (6809)
  • The number of bytes allocated for each I/O slot can be set to 4 (6800) or 16 (6809)
  • Three SS-50 slots

It’s no secret I’ve been slowly working on a 6809 based SS-50 system so the motherboard is the first step.  Until a working 6809 CPU board is ready there’s no way I can test it completely, so there are only engineering prototypes now.

Along with the new motherboards are SS-30 bus extenders that add slots 2-7.  This works with the existing motherboards too.

The SS-30 SD cards have arrived and don’t work, but I’ve yet to spend the time to debug them.  Again, these are engineering samples, so this is where bugs are shaken out and then production boards are ordered.

The 6809 CPU board is designed and I’ve been breadboarding portions of it.  There are still too many chips so I’m trying to simplify the logic a bit while still using 7400 series chips.  Using a small CPLD would greatly simply the design and get rid of all the glue logic but then it’s less vintage and many people won’t be able to make changes.

The design is nothing amazing, but makes a nice system:

  • 6809 running at 2 MHz
  • An 8K EPROM (they’re easy to come by) but only the top 2K (normal) or 4K will be enabled.  The default is 2K but the user can install one jumper to turn on the EPROM from F000 to FFFF.
  • Baud rate generator, but the shared Sx/baud rate pins are each selected by a jumper so you can add from zero to four of the extended addressing pins.
  • SWTPC compatible Dynamic Address Translation.  Extends the address bus by four bits.
  • Baud rate pins moved a bit so 1200, 2400, 4800 and 9600 can be put onto a single pin, freeing up the rest for extended address bits.
  • 128K of RAM!  Definitely not vintage.  It is selectable in 8K chunks for banks 0 and 1.
  • Uses standard SBUG.  I might add extensions like we did with SWTBUG but it remains to be seen.

I’m really hoping to get the chip count down, finalize a PC board and order prototypes within a week.  The goal is to have production versions at VCF East in mid-April.


SD Card, 6800/6809 Motherboard

Wednesday, December 24th, 2014

The prototype SD interface cards are here.  One minor board layout problem exists, so it’s a couple cuts and one jumper to fix.  The FLEX drivers are written but I just haven’t put it all together yet.  Lately I’ve been in a hardware mood, but will get back to software over the next couple of weeks.

Right now my CAD program is generating the Gerber files for the new 6800/6809 motherboard that should support the existing 6800 CPU card and also the 6809 CPU that I’m getting back to.  Prototype boards should arrive in about two weeks for testing.  The plan is to discontinue the existing 6800-only motherboard and only use the new one.

The other new board is a SS-30 expander that adds slots 2 to 7 using the expansion connector on the motherboard.  This board will work with both the existing and the new motherboards.


SD Card, 6809 Motherboard

Sunday, December 7th, 2014

I’ve been busy with lots of other things but have gotten some time for the 68xx related projects.

Engineering circuit boards for the SS-30 SD card have been ordered and should arrive this week.  Software has been moving forward too, as the sector read/write functions are all tested and the Flex drivers have been written.  The higher level utility functions have been moved into EPROM so the software has less to load.  Just need some time to sit down and glue it all together.

I also finished the schematic capture of the next version of the SS-50/SS-30 motherboard which adds support for both 6800 and 6809 based CPU boards.  Ie, it can be jumpered to set the I/O base address to 8000 or E000, drive RS2 and RS3, and change the number of addresses per SS-30 slot to either 4 (6800) or 16 (6809).  Hoping to get the PC board laid out this week but won’t rush out to order the boards until giving it a few more look-sees to make sure I didn’t miss anything.

Most people are asking about the 6809 board… it’s making slow progress and the schematic capture might be done by Christmas.

My intention is to have a production-quality 6809 based system in time for VCF East April 17-19th.  Setting a hard date forces me to make steady progress.