I have a GRiDCASE 3 laptop that has application software stored in EPROMs. It can fit up to 1Mbit of EPROM memory, but only 128KB are available at a time.

The ROM is mapped to a 128KB window at 0x8000h, I have an 8086 MS-DOS program and I want to read data from EPROM that is not currently visible.

This switching appears to be handled by the system BIOS (not manual hardware toggling), since on boot the BIOS reads all the data in the EPROMS and present it as part of the A:/ root folder. Taking the EPROM out of the socket makes the files disappear.

Is there a documented BIOS interrupt or API to select an EPROM bank? Maybe even a direct OUT call?

Any pointers to documentation, disassembly notes, or working code would be useful.