Mike's PCjr Page

Hi.

I have several games that support Tandy graphics, however, even though I have a functional Tandy modification on my PCjr, these games will give the error that a Tandy 1000 is not present. Does anyone here know what these programs are specifically looking for to identify if a Tandy 1000 is present or not? If it is a matter of some register setup, maybe I could setup the Jr using debug before starting the program, or write a small Turbo Pascal utility to that effect.

You need to disassemble the startup code to be sure, but there are a few standard things that programs usually look for:

• Machine ID byte. (Probably not a good candidate in this case.)
• BIOS copyright date - only works on the PCjr because there was just one BIOS revision. ;-0
• Copyright string in ROM - 'TANDY' might show up in the ROMs, and the code is probably looking for that.
• An extra return code from a BIOS function that only the Tandy machines have.

Mike

If this is ROM or BIOS based, I don't see how a fix is possible...

Walid

In that case the game needs to be patched.

You disassemble the code to find where it makes the decision. And then you just hard code the branch to do what you need it to do.


Mike

Yes, but easier said than done My 8086 assembly language skills are still embryonic, however I'll start poking around the code and see what I can find...