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430FX jumper settings for 3x multiplier?

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First post, by AST-AUTISMO

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Hi guys

I have an AST Advantage 8xx machine I'm trying to upgrade a little bit and get up and running. Currently it has a Pentium 133 installed and I would like to grab a non-MMX Pentium 200. However, jumper settings go only up to 2.5x suitable for a Pentium 166.

After a lot of reading i came across a post here that says that:

dionb wrote on 2018-01-12, 15:14:

The very first So7 boards had a single jumper for 1.5x or 2x (so 75-133MHz), if you can set 2.5x (i.e. 166MHz) that means you have at least two jumpers, which gives you four options: 1.5x, 2x, 2.5x and 3x. So even if the 3x setting is not documented, it's there. For 3.5x, Intel recycled the 1.5x setting. The P54C (Pentium non-MMX) reads it as 1.5x, the P55C (Pentium MMX) reads it as 3.5x. In other words, any board that has a setting for 166MHz can also do 200 and 233MHz with a suitable CPU.

So this may be true. I have settings for 1.5, 2.0 , 2.5 and "reserved". Would the Reserved configuration imply a 3x multiplier? I don't have a CPU to test with yet and so I'd like to have some idea if this would work (and safely) before spending the 40 or so dollars and waiting a month. See attached photo of the jumper config silkscreen.

Any hints would be welcome. Thanks!

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Reply 1 of 5, by mpe

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I think it is very likely the "reserved" is indeed the 3x setting. There are two signals (BF0 and BF1) and they are interpreted by the CPU and not by the motherboard or chipset. Considering the description. Position 1-2 seems to be "1" to BF0 and 5-6 "0" to BF1. Which should produce BF0 = 1 and BF1 = 0 or 3x multiplier. This is consistent with 1.5x (1,1) and 2x positions (0,1)

You should be able to confirm it with a multimeter. Also most CPUs should handle overclocking without too much risk, but your 133 MHz might be locked....

Blog|NexGen 586|S4

Reply 2 of 5, by Anonymous Coward

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Were 133s ever multiplier locked? As far as I know this only affected *some* MMX chips.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 3 of 5, by AST-AUTISMO

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Thanks guys, I will place the order. Presumably if the reserved setting doesn't work the Pentium 200 should work just fine at 166 right?

I'll update everyone once it arrives. Then I just need to find some more VRAM chips and maybe a pipeline burst module that will work (currently has a 256K async cache module installed)

Reply 4 of 5, by dionb

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Anonymous Coward wrote on 2020-08-04, 00:48:

Were 133s ever multiplier locked? As far as I know this only affected *some* MMX chips.

Oh yes, the SY022 chips were famous for it. I was very surprised recently to learn that some SY022 chips did let you modify the multiplier.

Reply 5 of 5, by AST-AUTISMO

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Hi guys,

Just checking in to report that I was successful. Using the reserved setting for the multiplier and the 66MHZ bus setting resulted in a successful boot at 200MHz using a non-MMX Pentium 200. Well, actually 199 Mhz but I won't split hairs 😀

Thanks for the help and reassurance.

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