I am an old computer user. I am 53, and I use old computers, as a collector of Tandy and TRS-80 computers. Tandy had the TRS-80 Model 100, one of the first laptops. For that machine, there existed a Disk/Video Interface that gave the '100 disk and big screen capabilities. The DVI were expensive, bulky and scarse, and I would like to rebuild their functionality with a Raspberry Pi. So I'm looking for assistance here.
The DVI appeared to be a (Z-80) computer on its own, receiving its commands via the parallel/system bus of the '100. In order to be able to handle the disk I/O, it had to load (BASIC) extensions to its ROM, in some kind of bootstrap fashion. But the screen management portion of the '100 was already build into the ROM-BASIC, so I assume it didn't need externally loaded extra software. So I would like to get that working, using the RasPi at the terminal end. I can get disk functionality in other ways.
The problem seems to me that the DVI is addressed in a parallel way as a terminal. Sadly, there is no mention of a protocol anywhere, but I have to assume it was something that was used before. The Model 100 could be used as a terminal, using VT-52 and maybe VT100 emulations. Tandy hardly ever invented something new... Maybe the chips used could give you some clues. (see below)
Assuming the above, it might boil down to:
1. making the proper connections and construction a cable
2. setting up the RasPi to correctly interprete the parallel signals and display the information on a sceen.
But of course, it's never that simple.
1. DVI Connector Pin Assignments. Since the cable was a straight-thru, we can assume that the '100 bus had the same signals.
2. DVI System Block Diagram. Maybe, from this schematic, someone can figure out how this thing worked. Only consider the video portion.
I have a Raspberry Pi (1) B, with 256 MB RAM. AFAIK, this is a very early/old version (suits me!) It has a 26-pin header.