Electronics > Projects, Designs, and Technical Stuff

Cloning a Tandy TRS-80 Model 1

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GK:
Oh, is there anyone out there who can tell me how to enable the "low resolution" 32 column display mode? I can't find any Level 1 info on this anywhere. Is it even possible in BASIC Level 1? This is an I/O operation and you have to toggle data bit 3 at address FF.

biff:

--- Quote from: GK on January 20, 2019, 03:12:12 am ---Oh, is there anyone out there who can tell me how to enable the "low resolution" 32 column display mode? I can't find any Level 1 info on this anywhere. Is it even possible in BASIC Level 1? This is an I/O operation and you have to toggle data bit 3 at address FF.

--- End quote ---

I believe this is strictly a Level II feature.

MustardMan:
I love your work! And you've made significant progress in such a short time - no got kids one assumes!

Anyway, reading about the 'expanded' memory that you intend to put on this PCB and the likely conflict with a genuine EI (if connected)... would it not be better rather than modifying the EI that you put a jumper on your PCB to restrict it to 16K? Then the EI can work without any changes, and it increases the ability for your board to be a true hardware clone...

Reading the discussion about the keyboard... that is a tough one. It could be that a CPLD/FPGA might be the only way to create a 100% true 'clone' - turning a PS2 keyboard into a close-as-can-be memory mapped one.

A project that intended something similar is on Hackaday.io, but it stalled and never seemed to progress. Shame. It might be interesting (or it might not) : https://hackaday.io/project/5565-trs-80-compatible-clone

I for one will be wanting to buy one of your PCBs! Any thoughts on creating a BOM, or if you'll do a kit of parts?

MM.

GK:

--- Quote from: biff on January 20, 2019, 03:31:55 am ---
--- Quote from: GK on January 20, 2019, 03:12:12 am ---Oh, is there anyone out there who can tell me how to enable the "low resolution" 32 column display mode? I can't find any Level 1 info on this anywhere. Is it even possible in BASIC Level 1? This is an I/O operation and you have to toggle data bit 3 at address FF.

--- End quote ---

I believe this is strictly a Level II feature.

--- End quote ---


OK, thanks, I thought so. You'd still be able to toggle low res mode in machine code though I'm sure, but I'm not that adept a TRS-80 user/programmer just yet.

GK:

--- Quote from: MustardMan on January 20, 2019, 09:27:29 am ---I love your work! And you've made significant progress in such a short time - no got kids one assumes!

Anyway, reading about the 'expanded' memory that you intend to put on this PCB and the likely conflict with a genuine EI (if connected)... would it not be better rather than modifying the EI that you put a jumper on your PCB to restrict it to 16K? Then the EI can work without any changes, and it increases the ability for your board to be a true hardware clone...

Reading the discussion about the keyboard... that is a tough one. It could be that a CPLD/FPGA might be the only way to create a 100% true 'clone' - turning a PS2 keyboard into a close-as-can-be memory mapped one.

A project that intended something similar is on Hackaday.io, but it stalled and never seemed to progress. Shame. It might be interesting (or it might not) : https://hackaday.io/project/5565-trs-80-compatible-clone

I for one will be wanting to buy one of your PCBs! Any thoughts on creating a BOM, or if you'll do a kit of parts?

MM.

--- End quote ---


Thanks for the interest  :)

I probably will be making the RAM size switchable between 16k and 48k because it appears that BASIC Level 1 doesn't properly recognize more than 16k, or at least doesn't accurately test it. For example I have my EPROM LUT address decoder coded to address either 16, 32 or 48k of RAM. I currently have a 256kbit (32kbyte) SRAM chip wired in. When I rewire the address decoder from 16k to 32k and type "PRINT MEM" to report on the free memory the computer responds with "-16897", which is actually (ignoring the negative sign) 32kbytes minus the actual free RAM in 16kbyte mode (512 bytes are reserved for BASIC).

I won't be proving any kind of kit but intend to complete and publish the design to the same extent as the PET-2001 clone.
   

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