Chkcpu wrote on Today, 14:47:

Ciao Elio, […]
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Ciao Elio,

I did a quick check on your original Acorp A-5VIA3P 12/02/97 Rev C2 BIOS, and it doesn’t support the Cyrix 6x86MX/MII when set to a x4 multiplier. I see this a lot in these late 1997/ early 1998 BIOSes.

The Cx6x86MX changes its CPU Model ID in the Device Identification Register 0 (DIR0) for each supported multiplier setting. The BIOS uses this register to identify the CPU and its multiplier setting, but the Cyrix ID table in your Rev C2 BIOS doesn’t go further than the ID for x3.5.
So when set to x4, the BIOS doesn’t recognize the CPU and can’t initialize it correctly.

The Unicore BIOS upgrade does support Cyrix x4 multiplier correctly. 😀

Cheers, Jan

Ciao, Jan
Thank you very much for your suggestions, actually I suspected that there was a problem when I selected the multi 4X, so much so that I had thought of trying a K6 200, first at a standard frequency 3X 66, then at a reduced frequency 4X 50, just to understand if the multi 4X works, but now thanks to you, I realized that it is a problem of non-recognition of the CPU, due to the BIOS that does not support faster CPUs, so I would avoid changing the CPU for the moment, and I would go directly to the tests with the "Linear Burst" active and the jumper closed.
The next step will then be the BIOS update, and then I would try the frequency of 266 MHz, that is FSB 66 and multi 4X, in this way the CPU would be in the specifications, since I use a Cyrix MII-333, although in reality that CPU is out of the factory as FSB 75 and multi 3.5X, in any case the frequency would be practically the same, 266 MHz against 262.5 MHz, so apart from a slight advantage for the RAM frequency at 75 MHz, for the rest it should be almost the same.
Finally, I'll try to cool the hottest linear controller better, I would try with an additional fan, apart from that I think this motherboard (and most of the VIA), were made with the full support of Cyrix CPUs, which instead shouldn't be on those i430, so if you don't overdo it with the frequencies, I think that around 266 MHz, it can work quite well, in the sense that there should be no problem, due to excessive temperature on the regulators, but beyond and up to 300 MHz, it could be close to the maximum bearable frequency, at least from what I remember.
For these reasons, I think that probably, it is not convenient to use K6-2-400 2.2V CPUs, or other slower 2.2V CPUs, because they pointed out to me, that it would heat up more given the greater difference between input and output current, that is 3.3V-2.2V instead of 3.3V-2.8V.
Greetings Elio