There isn’t any chance of being able to force this clock gen into 83mhz via software is there?

When you change the 14MHz crystal you will cause some essential things such as system timer to speed up, which will break a lot of software. The very least you must make sure that all the 14MHz outputs remain what they are. Other things wouldn't be a problem as long as the PLL itself will be able to handle the higher clock input which it might not. Datasheet will tell what range there is that is guaranteed to work.

Tiido wrote on 2021-03-05, 17:12:

When you change the 14MHz crystal you will cause some essential things such as system timer to speed up, which will break a lot of software. The very least you must make sure that all the 14MHz outputs remain what they are. Other things wouldn't be a problem as long as the PLL itself will be able to handle the higher clock input which it might not. Datasheet will tell what range there is that is guaranteed to work.

So the quartz idea is a bad one?

So messing with f2 is my only option?

According to the datasheet, this will screw up a ton of things. Your ISA bus clock, FDD clock, and if the motherboard has USB (looks like it doesn't) it will break USB as it requires a 48MHz clock.

In short, changing the crystal is a bad idea.

gnif wrote on 2021-03-06, 05:37:

According to the datasheet, this will screw up a ton of things. Your ISA bus clock, FDD clock, and if the motherboard has USB (looks like it doesn't) it will break USB as it requires a 48MHz clock.

In short, changing the crystal is a bad idea.

it has usb.

Okay. What about a software option for overclocking to 83mhz?

Is messing with that f2 pin my only hope?

Sphere478 wrote on 2021-03-06, 05:46:

Okay. What about a software option for overclocking to 83mhz?

None, machines of this era never had such ability.
Datasheet clearly shows your clock is programmed by the jumper settings and not via any communication bus.

gnif wrote on 2021-03-06, 05:57:

Sphere478 wrote on 2021-03-06, 05:46:

Okay. What about a software option for overclocking to 83mhz?

None, machines of this era never had such ability.
Datasheet clearly shows your clock is programmed by the jumper settings and not via any communication bus.

Do you agree that it appears that f2 pin needs to be ungrounded to open up the 83mhz option? Via the already present jumpers?

Sphere478 wrote on 2021-03-06, 13:57:

gnif wrote on 2021-03-06, 05:57:

Sphere478 wrote on 2021-03-06, 05:46:

Okay. What about a software option for overclocking to 83mhz?

None, machines of this era never had such ability.
Datasheet clearly shows your clock is programmed by the jumper settings and not via any communication bus.

Do you agree that it appears that f2 pin needs to be ungrounded to open up the 83mhz option? Via the already present jumpers?

The photo of the PLL shows that F2 (pin 20) appears to be left disconnected, hard to tell without pulling the chip to be sure. To get access to 83MHz you need to ground this pin, the datasheet shows that F1, F2 and F3 are all internally pulled high when disconnected, so to unlock 83MHz you need to pull it to the ground (ie, 0V). You would need to very carefully solder some fine wire on to do this, I would suggest using Kynar Wire (aka, wirewrap) as it's perfectly suited for this kind of mod.

gnif wrote on 2021-03-06, 14:22:

Sphere478 wrote on 2021-03-06, 13:57:

gnif wrote on 2021-03-06, 05:57:

None, machines of this era never had such ability.
Datasheet clearly shows your clock is programmed by the jumper settings and not via any communication bus.

Do you agree that it appears that f2 pin needs to be ungrounded to open up the 83mhz option? Via the already present jumpers?

The photo of the PLL shows that F2 (pin 20) appears to be left disconnected, hard to tell without pulling the chip to be sure. To get access to 83MHz you need to ground this pin, the datasheet shows that F1, F2 and F3 are all internally pulled high when disconnected, so to unlock 83MHz you need to pull it to the ground (ie, 0V). You would need to very carefully solder some fine wire on to do this, I would suggest using Kynar Wire (aka, wirewrap) as it's perfectly suited for this kind of mod.

I think it is connected to a wire below the chip.

What about connecting it to the f1 pin while it’s set to ground?

I’ve been doing tests on the jumpers.

I’ve been able to set these speeds

Here is the table:

Some other speed settings were from doing this:

Does it look like any of those speeds may be based on 83mhz?

http://www.pchardwarelinks.com/cpuspeed.htm

Evasive sent this but haven’t been able to get any clues from it yet.

Okay, so I set it to 450 which should be 75x6 and shorted pins f1 to f0 and f2 and no post

So I tried pins f1 and f2 and still no post. No short it posts at 450..

I wasn’t sure that 0 meant grounded but seems it does. And it seems the async settings don’t work.. any idea why?

Based on that it seems I may need to replace the clock gen with a different unit?

Hasn’t anyone come up with a universal clock generator you can wire in and take over a motherboard with?

Proof of concept. Unfortunately.

I was able to achieve the as of yet unattainable 330 mhz setting by shorting f0 to f1 while jumper was set to c200 aka 450 75x6. The short creating the setting 55x6 330

This unfortunately confirms that my theories about how it’s set are correct and that the async settings including the 83mhz setting aren’t working for some reason.

Any ideas why async settings aren’t working on this clock gen?

Sphere478 wrote on 2021-03-06, 16:28:

Proof of concept. Unfortunately. […]
Show full quote

Proof of concept. Unfortunately.

I was able to achieve the as of yet unattainable 330 mhz setting by shorting f0 to f1 while jumper was set to c200 aka 450 75x6. The short creating the setting 55x6 330

This unfortunately confirms that my theories about how it’s set are correct and that the async settings including the 83mhz setting aren’t working for some reason.

Any ideas why asuny settings aren’t working on this clock gen?

Sorry no, without having the motherboard on hand and a DSO to probe/verify there is no way to know. If you did have a DSO with a bandwidth of 100MHZ or better you could check the output of the PLL.

Sphere478 wrote on 2021-03-06, 15:56:

And it seems the async settings don’t work.. any idea why?

Async never did work on anything before PC100, to be honest it should have never been included at all.

Most early 75/83mhz FSB Socket 7 boards would run async with only Cyrix branded CPUs and even then I had strange stability issues.

Put in an Intel or AMD chip set async no post.

Just how it was, my manual even stated async for Cyrix only.

To run at 75 or 83 you need to leave the pci divisor at /2 not async

rmay635703 wrote on 2021-03-07, 03:37:

Async never did work on anything before PC100, to be honest it should have never been included at all. […]
Show full quote

Sphere478 wrote on 2021-03-06, 15:56:

And it seems the async settings don’t work.. any idea why?

Async never did work on anything before PC100, to be honest it should have never been included at all.

Most early 75/83mhz FSB Socket 7 boards would run async with only Cyrix branded CPUs and even then I had strange stability issues.

Put in an Intel or AMD chip set async no post.

Just how it was, my manual even stated async for Cyrix only.

To run at 75 or 83 you need to leave the pci divisor at /2 not async

Hello, do you remember the model of motherboard and cyrix CPU that worked in async pci bus mode ? I have Asus motherboard with Intel 430fx chipset which also doesn't post if I select async mode. I replaced clocker on it with one which can do 75/83 in both sync and async modes. I also have measured pci frequency in async mode and it definitely can do async.

P5/P6 class chipsets from intel never supported asynchronous bus operation, this feature was meant for other chipset manufacturers, that did support it at the time.

rmay635703 wrote on 2021-03-07, 03:37:

To run at 75 or 83 you need to leave the pci divisor at /2 not async

Yup, so be aware that you're running PCI out of spec.