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PC Chips 286 M216 Motherboard

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First post, by Fanatik

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I recently purchased a 286 PC Chips M216 Rev 1.2 motherboard along with a 25mhz cpu. I am under the impression that it doesn't support zero wait state. Is this a function of bios or a limitation of the board itself. Would it be possible to swap bios chips from a board that supports zero wait state? I really like the layout of this board and would like to use it.

Reply 2 of 26, by dieymir

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It's a limitation of memory speed. A 25Mhz. 286 will require very fast DRAM modules (<50ns) or a small amount of cache. Cache is done using SRAM memory chips that don't need refreshing and are much faster (<25ns).

You have a calculator here:

https://matrix.home.xs4all.nl/calc/waitstates.html

According to it you'll need at least 1 WS for 60ns DRAM memory modules. For 0 WS operation you need at least 28ns DRAM memory modules which, AFAIK, are not feasible.

Reply 3 of 26, by Fanatik

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There are plenty of people running 286's in zero wait state. It was also advertised heavily in Pc magazines in the 80's. I'm just wondering if I can swap bios chips so I can run my memory in zero wait state.

Reply 4 of 26, by feipoa

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I didn't realise PC Chips made 286 motherboards. Post a photo? I wonder what their first motherboard was?

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Reply 8 of 26, by Fanatik

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Here is a pic of the bios. Notice how there isn't an option to run the dram in 0 wait state?

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Reply 9 of 26, by Moogle!

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I've been curious as to whether or not the ram runs at the CPU speed on the faster 286s, or if it runs at the speed of the system bus. To get 0 wait states on a 25Mhz CPU, you would need 40ns ram, something I have never actually seen. For 20Mhz, you would need 50ns, which is rare as hens teeth and no one buying a 286 at that point was going to be buying something as expensive as 50ns ram.

16Mhz needs 60ns, 12.5Mhz need 80ns, 10mhz needs 100ns, 8Mhz needs 120ns, 6Mhz needs 150ns, and 4.77/5Mhz needs 200ns.

On the other hand, I may be completely misunderstanding what wait states are and how they work. I can find little actual information about this, at least nothing that is clear on the matter.

EDIT: Missed the third post in this thread. Nice find.

Reply 11 of 26, by Anonymous Coward

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Find out what kind of chipset your motherboard actually uses. PCchips normally relabels chipsets from other companies. Then see if you can find a MR-BIOS replacement. This might allow you to play with memory timings. Alternatively, you can try running AMISETUP V2.99 to see if there are any hidden features you can manipulate.

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Reply 13 of 26, by feipoa

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Fanatik wrote:

I believe Mr Bios is shut down. Couldn't I swap a bios chip from another board?

For this board, typically yes, if the chipset is the same.

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Reply 14 of 26, by Moogle!

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I thought 286 BIOSes were interchangeable, regardless of chipset? Or is that only for older BIOSes?

When I get my board I will dump mine.

Fanatik, was there a reason you chose that board over the other one that had a 25Mhz cpu on it?

Reply 17 of 26, by Moogle!

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Fanatik wrote:

I heard bad things about the M209. I heard it was slow, plus I didn't like the fact that the cpu is soldered in. I bet your bios won't have the option for zero wait state either.

Mine is the (219), not 209. 😉

Reply 19 of 26, by derSammler

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dieymir wrote:

According to it you'll need at least 1 WS for 60ns DRAM memory modules. For 0 WS operation you need at least 28ns DRAM memory modules which, AFAIK, are not feasible.

That's not correct. Calculation is "1000 / MHz = RAM speed in ns". E.g. 1000 / 25 = 40ns. Normally, it's ok if RAM is specified slightly slower, so 50ns should work as well (I run my 16 MHz 286 with 0 WS and 70ns RAM). If you add 1 WS, RAM can be 80ns instead of 40ns, but since the 286 has no cache, speed would equal a 12.5 MHz CPU then. The latter was actually the case with the few 25 MHz 286 that hit the market. They were slower than 16 MHz ones since no RAM fast enough for 0 WS was available.

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