Electronics > Projects, Designs, and Technical Stuff

Cloning a Tandy TRS-80 Model 1

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nick_d:
Not boring :)

To avoid damaging the expansion unit by lifting pins, could you just allow the expansion unit RAM to do its job and your RAM to do its job in parallel? It won't matter if two devices drive the data bus, providing they're driving the same thing to it. There might be issues with output-enable timing if it's driving the bus before the data has been read, though.

cheers, Nick

GK:

--- Quote from: nick_d on January 12, 2019, 11:37:57 am ---Not boring :)

To avoid damaging the expansion unit by lifting pins, could you just allow the expansion unit RAM to do its job and your RAM to do its job in parallel? It won't matter if two devices drive the data bus, providing they're driving the same thing to it. There might be issues with output-enable timing if it's driving the bus before the data has been read, though.

cheers, Nick

--- End quote ---


Thanks for the interest ;)

Problem with the old DRAM is that it was really slow. I think there would be nasty current spikes and EMI as the RAMs fight each other before they are outputting the same values.
 

GK:


German_EE:
I remember the old TRS-80 keyboard where each key was mapped to an address in memory, your scheme using an EPROM and a PIC is very elegant!

Looking forward to the day you run SCRIPSIT.

GK:
Thanks  :)

I'm currently laying out a little board for the PS/2 keyboard interface. This will be a universal design compatible with any TRS-80, not just my clone.

SCRIPSIT - know where I can download an audio file? I've been so engrossed with other aspects of this design that I haven't even started looking for software yet. I am about to nip out in 5 to get the paper and another breadboard from Jaycar. The next and final section to get breadboarded is the data cassette interface. Amazingly, despite the rats nest assembly on crappy cheapo breadboard, I seem to be getting the computer reasonably stable now. If it turns out to be stable enough to load and run a game or too, that would make for a cool initial Youtube video, I would think.


EDIT: found in ~30s : https://www.classic-computers.org.nz/system-80/software_cassette_archive.htm

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