rasz_pl wrote on 2022-01-31, 11:57:

Searching for UM82C480 will give you limited datasheet. At least it offers internal block diagram and pinout

Nice, thanks. It looks like the trace going to pin 19 of U52 goes to 141 of the 82C481, which is a ground. So the R32 is always connected and can't be turned on or off, so I was wrong about that.

Sooo what is this board really? 😀 Theretroweb still doesnt have it.
"486 LOCAL BUS ver1.0"
Latest datecode on soldered chip 92 week 11 = March 1992
Super custom reverse ISA "Local Bus slot". Its not Gigabyte Local Bus, Orchid Local Bus, not OPTi Local Bus, not ECS Local Bus, not even Acer Local Bus.
Its a brand new unknown early Local Bus variant Pre-VESA Proprietary 32-bit Local Buses?

@stephen_usher any chance on BIOS upload?