Hi egbertjan,

From your picture I can see that you have the Version 4.0 BIOS with a 08/02/95 date.
These August 1995 Award BIOSes didn’t have Am5x86-P75 support, but they do support the Enhanced Am486DX4 CPU.

There is a later Version 4.2 BIOS for your board that can be downloaded from:
https://theretroweb.com/motherboards/s/rectro … t-4s3#downloads

I’ve checked this 10/30/95 BIOS and it has indeed Am5x86-P75 support! 😀
This BIOS is just 3 month newer, so probably won’t have any other improvements than Am5x86 support.

Note that both the Ver 4.0 and 4.2 are non-Plug&Play Award v4.50G BIOSes, so they can use an UV-EPROM BIOS chip. Therefore it is quite possible your board doesn’t have a modern BIOS flashchip and you need an external programmer to store the new BIOS in an (E)EPROM.

When you need help finding-out which BIOS chip you have, peel back the Award sticker and post a picture of the top of the chip.

Jan

Thank you very much. Here is the picture of the BIOS-chip. Do you know wether or not I can flash this chip?

You cannot flash that chip directly from the motherboard. It needs to be erased with UV light (that's why the little window on the chip is covered with a label) and then flashed on a programmer. So the best option would be to flash a new chip if you have a programmer or have someone do it for you, that way you don't have to erase the original chip.

@TheMobRules, thanks. Yes this BIOS chip is indeed an UV-EPROM. This M27C1001 by SGS-Thomson is a 1Mbit (128KB) EPROM and was widely used on boards of that era.
Here is its datasheet:

This EPROM needs a programming voltage of 12.75V, so most (E)EPROM programmers will support this chip.

@egbertjan, where are you located? If you live in or near The Netherlands, I may be able to help you with this BIOS update.

Jan

Thank you very much Jan, you are very herlpfull. I indeed live in the Netherlands, in Drenthe. I would appriciate it very much if you could help with updating the BIOS. Can you let me know what steps I have to take?

Egbert Jan

egbertjan wrote on 2023-07-01, 14:10:

Thank you very much Jan, you are very herlpfull. I indeed live in the Netherlands, in Drenthe. I would appriciate it very much if you could help with updating the BIOS. Can you let me know what steps I have to take?

Egbert Jan

Okay, I send you a PM with the necessary steps.

Jan

From Chkcpu I received a chip with an update for the BIOS. I mounted the chip on the board and the result was completely OK as you can see on the photo's. The AM5x86-P75-S is now correctly supported. I am realy happy with this result.

Before update:

After update:

Before update:

After update:

After the update there was an extra setting in the BIOS: CPU burst write. Can someone tell what this is about and should it be dis- or enabled?

I know that Cyrix 486DX(2)(4) and Cx5x86 CPUs have a “Burst Write Cycle” feature that can be enabled or disabled via software. The “CPU Burst Write” option you see in the new v4.2 BIOS probably controls this Cyrix feature.

Enabling Burst Writes should increase performance but if it is a Cyrix only feature, it won’t do anything on AMD and Intel CPUs. But you can always try enabling it on your Am5x86 and see if it makes any difference. 😉

Cheers, Jan