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.

Nice!

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.

 

Real SWTPC Memory Board

Friday, September 26th, 2014

For fun, I put a real MP-8M memory board into our test motherboard and ran memory tests:

SWTPC_MP8M_1

You can see the power supply above the board in the background… 1.03 amps!  That’s with only 4K populated, versus our 64K board that draws about 100 ma.

Memory tests ran for a couple hours without a hitch, so this shows our CPU and motherboard will work properly with vintage boards.