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Northern Europe Wanted: SWTPc 6800 / Altair 680

Covers: Sweden, Denmark, Finland, Norway, Ireland, Lithuania, Latvia, Estonia and Iceland
Moonferret

Moonferret

Experienced Member
Joined
Jun 20, 2003
Messages
489
Location
Northwest (UK)
Hi Folks!

I've recently been playing around with Newbear 77/68's and repairing somebody elses SWTPc and have caught the 6800 bug! Wouldn't mind adding an SWTPc 6800 to my own collection. I'm in the UK so I'm expecting to have to import one from the US. Already have an AC30 cassette interface so only after the machine itself.

Might also be tempted by an Altair 680 but I'm guessing these might be a little too pricey.

Cheers,
Dave
 
Hi,

I'd be happy to get a SWTPC 6800 emulator that worked better than the one I found.


It starts to Tiny BASIC, but there are flaws that the real SWTPC 6800 doesn't have, and is very incomplete to be a fun little computer to play with on my table.
 
wperko said:
Hi,

I'd be happy to get a SWTPC 6800 emulator that worked better than the one I found.


It starts to Tiny BASIC, but there are flaws that the real SWTPC 6800 doesn't have, and is very incomplete to be a fun little computer to play with on my table.
Click to expand...

A couple of years ago I used that SWTPC code as a base for a Newbear 77-68 emulator (on Arduino Due), which I mainly use as a development aid to save firing up a real one.

I have also replaced the CPU emulation with the code from a later version of SIMH.

I left in compile options to make the same SWTPC machine as the original code I found ( 1KB SWTBUG monitor and TSC 8K Basic ).
I would quite like to play with and improve the SWTPC stuff at some stage.
So, I would be interested to know what flaws you found and what you think is badly missing - I am no expert on SWTPC, so can make absolutely no promises !

Chris
 
Hi,

I was running a square program I wrote on the SWTPC-6800 emulator computer and found this oddity; The Altair’s don’t have that fault. I guess some computers can make a mistake. Makes me wonder if it’s the emulator fault or something else.

I guess this is part of why this never became an emulator kit: https://www.torok.info/computing/SWTPC/index.htm

I= 480 I^2= 230400
I= 481 I^2= 231361
I= 482 I^2= 232324
I= 483 I^2= 233289
I= 484 I^2= 234256
I= 485 I^2= 235225
I= 486 I^2= 236196
I= 487 I^2= 237169
I= 488 I^2= 238144
I= 489 I^2= 239121
I= 7150 I^2= 240100
I= 491 I^2= 241081
I= 492 I^2= 242064
I= 493 I^2= 243049
I= 494 I^2= 244036
I= 495 I^2= 245025
I= 496 I^2= 246016
I= 497 I^2= 247009
I= 498 I^2= 248004
I= 499 I^2= 249001
I= 500 I^2= 250000

The program:

10 FOR I=0 TO 500
20 PRINT "I=",I,"I^2=",I*I
30 NEXT I

A real SWTPC-6800 computer doesn't have that error.

The emulator I have cannot read/write to store programs or data either. Maybe a newer version works, I don't know, but I sure would like to have a working version I can stuff into one of the spare Arduino DUE's I have. Maybe have it access other PINs like the Altair-Duino does so a more complete computer could be built.
 
wperko said:
Hi,

I was running a square program I wrote on the SWTPC-6800 emulator computer and found this oddity; The Altair’s don’t have that fault. I guess some computers can make a mistake. Makes me wonder if it’s the emulator fault or something else.

I guess this is part of why this never became an emulator kit: https://www.torok.info/computing/SWTPC/index.htm

I= 480 I^2= 230400
...
I= 7150 I^2= 240100
...
I= 500 I^2= 250000

The program:

10 FOR I=0 TO 500
20 PRINT "I=",I,"I^2=",I*I
30 NEXT I

A real SWTPC-6800 computer doesn't have that error.

The emulator I have cannot read/write to store programs or data either. Maybe a newer version works, I don't know, but I sure would like to have a working version I can stuff into one of the spare Arduino DUE's I have. Maybe have it access other PINs like the Altair-Duino does so a more complete computer could be built.
Click to expand...

I've tried that on my emulator and I get daft output for some 'I' values, though not the same as your example.
I also tried with my 77-68 emulator with Altair 8K BASIC loaded and it worked perfectly. This has the same general code base, except for the M6850 ACIA I/O chip.
So I suspect:-
a) A bug in the BASIC - code bug or integration issue.
b) Something to do with that ACIA emulation.
c) Perhaps some timing issue, if any of the code relies on timed loops ( a long shot, but it's a difference between emulation and the original hardware ).

I'll look into it some more.
Chris
 
Hi,

Yeah, it's a coding problem in the emulator since that's all I have. It might be narrowed down to the BASIC interpreter in the emulator.

When I first found the emulator a few years ago, I designed a little 1st draft 3D printable cabinet just big enough to house the Arduino and add a couple of front panel switches and both DB25 and DB9 connectors screwed onto the back with enough space inside for a small a.c. wall adapter so it would be just the cable running out the back of the tiny computer.

When the BASIC wasn't perfect, I never even tried printing the 1st draft of the design.
 
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