Electronics > Projects, Designs, and Technical Stuff
Cloning a Tandy TRS-80 Model 1
nick_d:
Is it Microsoft BASIC? There is a disassembled source code around for NASCOM Z80 BASIC, probably a similar version to what was used in the TRS-80 (single precision only, lacks commands such as RENUM). It would be relatively straightforward to compare this with Level II BASIC and disassemble only the missing parts. Then patch it for lower case. Some day I plan to disassemble the the most modern CP/M version like this, since the extra is not all that much.
cheers, Nick
kizmit99:
Yep, TRS80 Basic was licensed from Microsoft... Seem to recall some BS story about Bill G. writing it over one weekend or some crap like that...
oPossum:
I think it was the first version of the Altair 8800 BASIC that was written in a short amount of time and tested on an emulator running on some model of DEC PDP.
netdudeuk:
--- Quote from: oPossum on February 06, 2019, 04:44:33 am ---I think it was the first version of the Altair 8800 BASIC that was written in a short amount of time and tested on an emulator running on some model of DEC PDP.
--- End quote ---
At least this is true. They created a punched tape which Bill took to demo.
BartH:
--- Quote from: nick_d on February 06, 2019, 04:25:51 am ---It would be relatively straightforward to compare this with Level II BASIC and disassemble only the missing parts. Then patch it for lower case.
cheers, Nick
--- End quote ---
No need for disassembling the ROM, this has already been done. The Model 1 did have lower case in its character ROM but was not able to display it, due to the 6 bit memory. When the need for Word Processing came (the next big thing in 1979 or so) Tandy came up with a lower case kit. It included the memory chip, a new character ROM and a cassette with a driver. As disk drives became cheaper and DOS'ses more common the drivers became part of the operating system.
So for reasons of compatibility with old software I would suggest to focus on adding (emulated) hard drives like the FreHD and using LDOS or NewDos/80 for lowercase drivers. The autoboot Model 1 rom's are also readily available (back in the day you booted initially from floppy before loading a HD-driver).
If you really want to use the Model 1 with lowercase and no floppy or HD you should change 1 byte in ROM: address 0x0473h contains 0x38h (JR,C) and should be changed to 0x18h (JR). This mod bypasses some code that essentially changes lower case back to upper case.
BTW later Model 1's contained the character rom in a socket so it didn't need desoldering when updating with the RS Lowercase kit. The later 'Japanese' Model 1's already contained the missing 7th bit and had a better character ROM. You still needed a driver or DOS to display the lower case characters.
Bart
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