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.

Life In The Fast Lane

Wednesday, October 29th, 2014

Sorry for no updates for a while, but my son’s Eagle Scout project is this Saturday so we’ve been working on preparations for it most of the last few weeks.

But on to the fast lane!

For fun, I replaced the 6800 with a 68B00 and cranked up the speed on the CPU board.  The variable resister and capacitor combo limited it to 1.791 MHz, but the CPU worked great!  The 6850 in the serial board was still working, but I should put in a 68B50 just to be sure.  I loaded up Microsoft 6800 BASIC and then an old biorhythm program and definitely noticed the faster CPU.

One place the CPU speed made a big difference was entry of programs.  I have a bunch of BASIC program files on my desktop machine and simply upload the ASCII files while in the BASIC interpreter.  BASIC tokenizes each line and then inserts it into memory, so if the interpreter is slow, then the next line starts arriving before it’s ready to receive it, resulting in corrupted lines.  To overcome this, it’s customary to insert a big delay after each CR/LF to allow the interpreter to process the line, but this really slows things down.  Now I can greatly reduce the delay, speeding up the transfer rate.


Oh, and I’ve been stocking up on 2 MHz support chips for another project, but it’s too early to say much.


Progress on Loading FLEX from SD Card

Thursday, October 16th, 2014

…and other stuff.

I’ve got Michael Evenson’s SWTPC emulator up and running, so now I’m slowly working from the top down (writing FLEX drivers) and the bottom up (drivers in EPROM to do SD disk reads/writes).  More and more of the disk logic is going into EPROM as it’s being properly tested and debugged.  Maybe by next weekend I’ll have something running.  The actual board hasn’t been designed yet but it’ll be easy to lay it out once the software is working.

The other big project is my son’s Eagle Scout project in a couple weeks, so that is high priority for now and consumes a fair amount of time.

I’ve also been using the 3D printer a lot more recently.  There are some vintage computer pieces that just aren’t made anymore and hopefully I can fabricate them myself.