I’m just posting to ask if this is feasible for someone with limited knowledge about hardware.
Subject is an OLD Allen Bradley socket 7 SBC (6189-1cpu233) with an annoying feature of a fixed output resolution! I actually have two of these boards and both have a different fixed resolution, (640 x 480 and 800 x 600). Both BIOS versions are identical but there is about 10% of the raw HEX that’s different. I’ve swapped these images from one to another and the fixed resolution changes so I’m confident this issue lies within the BIOS.
There is a feature in the CHIPS 65550 display drivers that changes the output mode to “CRT” vs “LCD” that unlocks this fixed resolution but reverts after restart. Meaning the BIOS writes to a register in the display IC to the fixed LCD mode on power up.
I can see this register information in the datasheet. → https://www.versalogic.com/wp-content/themes/vsl-new/assets/resources/support/pdf/65550.pdf (FR01 CRT / FP Control Read / Write at I/O Address 3D1h) page 287.
So the question is, is it a matter of finding this register write function in the BIOS file and changing the value it writes? I’m assuming I can’t just search for “3D1h” or “FR01” in the BIOS dump. Is it possible to disassemble and find this function? Would the address be clearly readable or added/masked in some way? I’m rather limited here and just want to know if this is even possible to do.
Or, is it possible to add a write function to the tail end of the BIOS to simply set the value to something else, assuming I can figure out how to write such a function?
I’ve posted this question on Vogons NEED BIOS HELP Rockwell Automation 140420-030 Allen Bradley 6189-1CPU233 CPU Card SBC \ VOGONS and the BIOS file dumps are at the bottom of the last post.
So, possible, or fool’s errand? Thx for any advice!