On 8/30/20 10:12 AM, Erik van der Tier wrote:
Hi All,
After a lot of work fixing issues with string defines, and specific issues with
generating opcodes for SUB H vs SBB H, I’ve now got a assembler source for the
T102 rom. When assembled it is almost completely binary identical to the
original T102 rom. The only difference should be that I changed 100 in to 102
in the basic prompt. When compared to a dissasemble from the T102 rom included
in VirtualT you’ll notice I’ve reverted the VirtualT back to Microsoft as well.
There are now only 3 bytes difference. The last byte is the 0 that is not 2
(for the model number). The other two bytes are two addresses that are called
which are different in the rom in my actual 102 than they are in the Rom that
is part of the Virtual T distro. I’m not sure where those to differences come
from.
I do have a rather long list of L<address> labels defined in this current file
which I’ll either will have to find good names for or just accept hard addresses in
the source. I’m currently undecided there. There are also still some unlabled F***
addresses (please note that the *** are for the rest of the address and not for some
nasty word here).
But I really wanted to get this baseline right, so now I can always quickly
compare after more elaborate changes and see if the rom should still be ok
(until I start working on custom roms of course).
Anyway, I hope some of you will find this result useful. Now I really need to
do the hardware mod for my Rex so I can start loading my own rom versions :)
Wonderful!
I made a little pcb to make it a little more convenient to use the rex
main-rom feature:
http://tandy.wiki/FlexROM_102
The main point of it is you can remove the rex and revert to the
internal rom without opening the case again. But it's also handy that
the internal rom is an eeprom instead of a uv eprom or the original mask
rom. You can re-program it any time using a test clip (though that does
require opening the case).
I don't make any great claims that it's worth the bother of building it,
just that it exists and I like it. It's more worth it on 100 because 100
already has a socket on the motherboard and 100 needs the non-standard
pinout translated to use any other eprom or eeprom.
102 you could just stick a 27C256 directly in there, or no chip if you
don't care that it doesn't run without rex anymore.
--
bkw
