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Model 4P ROM

D

dittman

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I have a Model 4P motherboard with a non-standard EPROM:

Model 4P Modified ROM - 1.jpg

Does anyone know if the part number is a standard 4P part number? I can't find it online If it's the standard 4P ROM part number I'll not bother undoing the mod to read the EPROM.

I did check the Model 4P Service Manual and it's not listed there but Radio Shack might have had ROM updates that weren't reflected in the SM.
 
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Shops and the factory would never do a mod that looked as bad as that. This could have been a pre-pro used for testing in R&D, or it could have been Frank horsing around with BIOS which he did a lot of way back when. It's not production, whatever it is. My guess is pre-pro.
 
I've seen several of those particular ROMs. Frank's and even a few other places I have read alluded to some errors in how they handled the newer floppy drive controller in the GAs. Not sure if RS ever fixed it, but Frank's XROMs did.
 
I'd hope they did, I'm sure if the right person got it they could even help the family out with proceeds from them. I'd pay for one today if I knew they would get them.
 
Holding 'V' when booting that rom shows it to be version 1.15 11-Oct-83. This is a week earlier than the 4P ROM I have which is 1.16 18-Oct-83.

Cool to see a different version, thanks!

It'll be interesting to disassemble the code and see what difference a week made.

[ Edit: I think the XROM was only for Model 4 and 4D systems so it wouldn't be found on a 4P ]
 
gp2000 said:
Holding 'V' when booting that rom shows it to be version 1.15 11-Oct-83. This is a week earlier than the 4P ROM I have which is 1.16 18-Oct-83.

Cool to see a different version, thanks!

It'll be interesting to disassemble the code and see what difference a week made.

[ Edit: I think the XROM was only for Model 4 and 4D systems so it wouldn't be found on a 4P ]
Click to expand...

Thanks for checking. We need these different ROMs archived somewhere.
 
Decided I better look at the differences between 1(15) and 1(16) before it gets forgotten. I'm pretty sure there are no code differences, just an alteration to a message. Well, and the version number change. I'm not exactly certain, but I think the 1(15) ROM would say "Loading ROM Image" while the 1(16) ROM simply says "Loading".

It appears this was known back in the day thanks to disassembly work by Adam Rubin. You can find his files with a Google search for:

4P Boot ROM Disassembled (19xx)(Adam Rubin)[Accompanying Files][BAS]

With any luck that will find the .zip archive with his disassembly comments in them.
 
I wonder why they made that simple change to just one message. Was it to make the ROM match the documentation (I haven't looked at the disassembly).
 
My wild speculation is that someone saw the "Loading ROM Image" message and decided they didn't want to so openly reveal that the disk contains a copy of the Model 4 ROM.
 
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