Hi there everyone!
As everyone knows the Tandy 1000 SL machines allow only 640KB RAM onboard, and a part of that memory is reserved for video. The amount of reserved memory is defined by what is configured at the serial EEPROM.
So i've been thinking about this:
1. ROM BIOS must have a RAM check routine and then reserve the amount for video on the top end RAM.
2. ROM BIOS must stop checking after 9FFFFh physical address, as the motherboard does not support any more than that.
3. Tandy 1000's must have special circuitry that map the reserved video memory to be mirrored on the B000h segment for monochrome and CGA compatibility.
4. C000h and D000h are allowed for option ROM's and/or UMB's.
5. E000h segment for DOS/DESKMATE ROM and must have additional circuitry for page flipping to access the rest of the DOS/DESKMATE ROM; F000h segment for system BIOS.
6. A000h segment can't be accessed by Tandy 1000 SL at all, unless special hardware is used, like a VGA card, that includes RAM and a BIOS to actually use it.
So points 2 and 6 are the most interesting to me. Using a lotech 1MB RAM card and adding memory on the A000h segment does nothing at all and no software can find it. So i've been wondering if the Tandy 1000 SL system BIOS can actually be patched to force detection up to AFFFFh.
The point of this is to actually use the A000h segment for video memory, to allow a Tandy 1000 SL to have the full 640kb for DOS, much like a 1000 TL does.
I see 3 things that stop me from doing this:
1. I have no idea how to properly disassemble ROM BIOSes, as i only done that to .EXE and .COM files.
2. If i manage to successfully disassemble the BIOS, i have to actually patch it correctly, and that could be difficult as i am inexperienced with ASM code.
3. Even if i manage to do the 1 and 2 points correctly i would have to find compatible chips and burn them to swap the originals on the motherboard.
Any help is appreciated, whether its advice, tools or whatever. You can also call me stupid, if you think the idea is stupid or otherwise impossible, but make your case why that is.
As everyone knows the Tandy 1000 SL machines allow only 640KB RAM onboard, and a part of that memory is reserved for video. The amount of reserved memory is defined by what is configured at the serial EEPROM.
So i've been thinking about this:
1. ROM BIOS must have a RAM check routine and then reserve the amount for video on the top end RAM.
2. ROM BIOS must stop checking after 9FFFFh physical address, as the motherboard does not support any more than that.
3. Tandy 1000's must have special circuitry that map the reserved video memory to be mirrored on the B000h segment for monochrome and CGA compatibility.
4. C000h and D000h are allowed for option ROM's and/or UMB's.
5. E000h segment for DOS/DESKMATE ROM and must have additional circuitry for page flipping to access the rest of the DOS/DESKMATE ROM; F000h segment for system BIOS.
6. A000h segment can't be accessed by Tandy 1000 SL at all, unless special hardware is used, like a VGA card, that includes RAM and a BIOS to actually use it.
So points 2 and 6 are the most interesting to me. Using a lotech 1MB RAM card and adding memory on the A000h segment does nothing at all and no software can find it. So i've been wondering if the Tandy 1000 SL system BIOS can actually be patched to force detection up to AFFFFh.
The point of this is to actually use the A000h segment for video memory, to allow a Tandy 1000 SL to have the full 640kb for DOS, much like a 1000 TL does.
I see 3 things that stop me from doing this:
1. I have no idea how to properly disassemble ROM BIOSes, as i only done that to .EXE and .COM files.
2. If i manage to successfully disassemble the BIOS, i have to actually patch it correctly, and that could be difficult as i am inexperienced with ASM code.
3. Even if i manage to do the 1 and 2 points correctly i would have to find compatible chips and burn them to swap the originals on the motherboard.
Any help is appreciated, whether its advice, tools or whatever. You can also call me stupid, if you think the idea is stupid or otherwise impossible, but make your case why that is.