On 10/26/2024 5:27 PM, Royce Taft wrote:
Along the same line, I’ve been thinking of reverse engineering the
DVI’s firmware (BIOS) and software (DOS which is loaded into RAM by
the BIOS) to the extent that it could be modified to utilize the
second side of a disk once the drive is changed out for a double sided
one.
I’m fairly certain that the side select signal on the floppy interface
is connected to a latch IC used for various system controls. If that’s
the case, the single sided drive limitation is one of
firmware/software, not hardware (besides the disk drive itself). I say
I’m only fairly certain since the schematic is very difficult to read.
The scan of the service manual floating around in various repositories
is not exactly high resolution, which makes the schematics practically
illegible. There is a user in the Tandy discord who is planning on
scanning the schematics from their copy of the service manual this
weekend.
It would be a fun project to gain a little more exposure to Ghidra,
especially with “overlays” in the memory map such as the memory
banking scheme used by the DVI and the region of RAM which will
contain DOS once the disk is read at boot.
Is there a place to stay up to date? After showing my DVI at Tandy
Assembly this year and playing with it a bit, I'd really like to better
understand the HW (maybe reverse engineering the schematic, etc.) and
I'd love to keep updated on this effort.
Jim
