Electronics > Projects, Designs, and Technical Stuff
Cloning a Commodore PET-2001
kizmit99:
--- Quote from: GK on June 09, 2018, 06:52:37 am ---I'm eager to get this project done and off the bench now as I have the circuitry for the TRS-80 clone pretty much done on paper now. Should be able to post some preliminary breadboard TRS-80 action in the not too distant future...... :D
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Sweet! :-+ :-+ :-+ Very interested to see where you take that one - I've always had a soft spot for the TRS-80. It was my first computer (in '78 I think), I did so much hardware hacking on that poor machine it no longer looks anything at all like the original. Still have it, plus another I bought from a friend sometime in the '90s - both still worked when last powered up (about 12 years ago :().
Recently I used cloning the TRS-80 as a project to get up to speed on FPGAs, the plan is to do up a PCB with that design (and the minimal supporting analog hardware (like the cassette interface)) to get up to speed on where PCB tech is today. The last time I did a PCB I think the layout and first prototype boards where something like $50K a pop (very early '90s, pretty high density mil-spec board admittedly) - so the thought of getting prototypes for $5 is just astounding to me... Anyway, looking forward to see your take on the TRS-80!
GK:
I thought mention of the TRS-80 might get a bite :) - that was quite a popular machine back in the day, particularly in America, the home of Radio Shack. I wonder how it compared to the PET?
My most tedious task so far for the TRS-80 project was manually writing the character set binary file. Unlike the PET, the TRS-80 didn't use a generic/jellybean EPROM for the character set, but used a Motorola mask ROM which was factory-programmable with the customers supplied character set.
I couldn't find an image binary file of this ROM on the net, but I did find nice graphic of the individual characters resolvable down to individual pixels. The TRS-80's character set is more primitive than the PET's, but that block graphics mode made it a lot more flexible for games and stuff. It's just a pity that the original designers didn't use the vertical video sync like the PET designers did as a CPU interrupt as a way of generating flicker-free writing to the screen.
I intend to functionally duplicate the whole of the TRS-80 model 1 including the expansion interface (with 48k of RAM total), with the exception of the floppy disc controller as the chip for that function is now only available NOS.
On the topic of character sets, I'm currently working on the documentation for my PET build - here is how I mapped in my PS-2 keyboard interface (as straightforward and logical as practical) the PET's 73 keys/functions to a modern keyboard layout. I've printed this out and laminated it to serve as a handy look-up card/reference when typing, though it's mostly only needed when you need to find a shifted graphics character.
kizmit99:
It sounds like you did exactly what I had to do for that font ROM - at least it was only 5x7... It sounds like you've already done it, but if not I can provide a hex file with the "floating a" if you need it.
My plan for the floppy controller is to emulate the WDC1771 with an Arduino Mega talking to a flash card.
OK, back to your current project... I'm gonna have to steal your keyboard template idea. It will beat going back to the vhdl file to figure out where I mapped the Break key :)
ebastler:
--- Quote from: GK on April 26, 2018, 02:45:15 am ---The (Z80) TRS80 model 1 is next on my list. I don't think that there are too many other "mini" computers from the era which can be cloned this way (not requiring NOS chips no longer manufactured).
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How about the Apple I and II? Somewhat similar to the PET, of course. But digging into Wozniak's graphcics design may be worthwhile?
james_s:
Somebody already did clone the Apple I, not sure about the II, that may be reasonable to try.
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