🚀 go-pugleaf

In article <1g4ul8INN2em@violet.csv.warwick.ac.uk>, esrej@csv.warwick.ac.uk (Mr
L A J Davis) writes: 

> I purchased a 486 motherboard fitted with a 486DX2 50MHz cpu. Unfortunately
> with no extra cooling the system fails to complete its bootup proceedure.
> The board is fitted with 33.3MHz crystal that can be replaced presumably
> for the different 486 cpu's the board is able to support.
> By cooling the cpu with a cold can out the fridge(very scientific) and
> I have managed to briefly run norton si which claims my processor is
> a 67MHz 486. My guess is that the crystal should be 25MHZ for the cpu
> to operate however on contacting the supplier he claimed that the crystal
> frequency didnt matter so long as it is high enough and reckons i need a
> 50 or 80 Mhz xtal which he is posting to me. Is this assumption correct?

My Taiwan motherboard with 486DX2-66 has a crystal of 33.33MHz. The
documentation prescribes a 25MHz crystal for a 50Mhz DX2 and a 50Mhz version
for a 50MHz DX. Also some jumpers have to be set.

> Logically I would say that the cpu frequency is directly related to the
> xtal frequency and therefore, as I have a dx2 50 the xtal should be 25MHz
> (or possibly some multiple of that)

This makes sense to me. Though I still wonder where my DX2 get's its 66MHz
clock from if the crystal runs at 33MHz only. Does it contain some internal
clock doubler circuitry? 

Regards, <kees>

PS. There is a fan right on top of the CPU's cooling fan.