I have a pretty uncommon RE321 network card (ISA, 16 bit) for my 386 build and I want to use it as a base for PROM for XT-IDE BIOS.

The label under the EEPROM socket says 27C64 that's why I supposed it supports only 8KB (64kbit) ICs. I have one 32KB (27C256) IC put in 3COM card with 12KB XT-IDE version on it. It works on 3COM and did not on RE321 that's why I wanted to give a try to 8KB version.

I put it on AT28C64 chip and it worked (I spent a day on that, but more on that later).

The problem is Checkit detects that XT-IDE occupies 16KB or 32KB of RAM depending on the initial address I set on my card via jumpers (C800 or CC00 give me 16KB, D000 - 32KB). The BIOS just duplicates 2 or 4 times (seems like address selection mechanism uses one or two extra address bits incorrectly.

Can I prevent that somehow?

On a sidenote... I started experimenting with XT IDE based on Necroware Youtube videos. He used the old versions of XT-IDE, flashing them directly without configuration. I repeated this process for my first build and it went well, but when I was searching for the XT-IDE firmware again, I found the fresh builds. They say that BIOS should be preconfigured but I did not pay much attention to it as I thought that if it worked without configuration it should work later.

I spent a day trying different configurations of memory and cards, duplication of BIOS on the same IC or shortening high memory address pins with GND! I suspected my network card isn't working - but Checkit showed me XT-IDE signature with 55 AA in the beginning! It just should have been working but it did not... Until I took 8KB version from the old XT-IDE package (the one from 2013).

Another interesting problem - after I was playing with IC swapping between two cards I tried to read and write the BIOS on AT28C64 one more time. I was surprised when I extracted it out of 3COM and saw it reads as FF AA instead of 55 AA. I don't know if it was a glitch or more intelligent 3COM card just reflashed the first byte to spoil the boot signature.