Electronics > Projects, Designs, and Technical Stuff
Cloning a Tandy TRS-80 Model 1
biff:
--- Quote from: GK on January 04, 2019, 01:38:50 pm ---
That would be awesome. I don't see a problem with wiring either your adapter unit or the original MCM6670 masked ROM to a 27XX footprint and reading it with your TL866. I use the same programmer.
Here is how you'd wire it. I'd use a machined-pin IC socket in place of the 2716, and plug that directly into the TL866. It's easy to solder wires to the pins from the top.
EDIT: oops, don't connect anything to A10.
--- End quote ---
Well,
I tried using every 2716 configuration available in the TL866 database, and every one of them resulted in nothing but 255's after a read.
See attached picture how I rigged it up.
At worst, I was expected jumbled data, not nothing at all.
Jim
GK:
--- Quote from: biff on January 07, 2019, 01:05:32 am ---
--- Quote from: GK on January 04, 2019, 01:38:50 pm ---
That would be awesome. I don't see a problem with wiring either your adapter unit or the original MCM6670 masked ROM to a 27XX footprint and reading it with your TL866. I use the same programmer.
Here is how you'd wire it. I'd use a machined-pin IC socket in place of the 2716, and plug that directly into the TL866. It's easy to solder wires to the pins from the top.
EDIT: oops, don't connect anything to A10.
--- End quote ---
Well,
I tried using every 2716 configuration available in the TL866 database, and every one of them resulted in nothing but 255's after a read.
See attached picture how I rigged it up.
At worst, I was expected jumbled data, not nothing at all.
Jim
--- End quote ---
That a bit disappointing. Other than double checking the wiring, which I'm sure you've done already, I'm not sure what else to suggest. When I get some time I'll have a play with my own TL866 and the 2716 configurations.
GK:
Well, my Z84C0006 arrived yesterday afternoon, and holy crap, after some hours of frustration it is now actually alive, although I'm a bit paranoid about even breathing over the breadboard at this stage ;D
Basic Level I just boots up with a blank screen and a "READY >" prompt. Basic Level II boots up with the question: "MEMORY SIZE?" - not sure ATM what kind of entry it is waiting for. I currently only have the basics of the keyboard matrix interface operating. I can assert any keyboard character by jumpering/poking between the keyboard scan output and scan input matrix lines on the breadboard, but that's not very usable at the moment as trying not to get multiple instances of the wire-poked character is next to impossible. Next up I'll have to adapt the PS2 keyboard interface design that I developed for my PET-2001 clone for the TRS-80.
I also had to add another 74HC74 IC to the video generation circuitry because I originally did not fully emulate the original video blanking function when the CPU takes control of the video memory. When the CPU relinquishes control of the video memory the reactivation of the CRT electron beam needs to be delayed by two parallel-input load cycles of the serial-output shift register to ensure that when the beam turns back on it won't initially scribe several erroneous pixels. This prevents snow-like artifacts being produced on the screen when intensively updating the video memory.
Aside from the data cassette serial interface, which I have not yet implemented, this then pretty much verifies the CMOS clone design.
oPossum:
--- Quote from: GK on January 08, 2019, 01:56:46 am ---Basic Level II boots up with the question: "MEMORY SIZE?" - not sure ATM what kind of entry it is waiting for.
--- End quote ---
'Enter' for default. It will then ask "CASS?", 'Enter' for default again. Then you will get "READY>".
kizmit99:
Looking good :-+
All the "Memory Size" prompt is looking for is where YOU want the top of memory to be (assuming it's not at the top of physical memory) in decimal of course :o. So you can reserve some room for non-Basic stuff.
You can just hit enter and it will set it to the top of physical memory.
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