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- Newsgroups: sci.electronics
- Path: sparky!uunet!mcsun!sun4nl!spider.research.ptt.nl!research.ptt.nl!walvdrk_r
- From: walvdrk_r@research.ptt.nl (Kees van der Wal)
- Subject: Re: 486DX2 Crystals
- Message-ID: <1992Dec12.003507.1@research.ptt.nl>
- Sender: usenet@spider.research.ptt.nl (USEnet News)
- Nntp-Posting-Host: dnlts0.research.ptt.nl
- Organization: PTT Research, The Netherlands
- References: <1g4ul8INN2em@violet.csv.warwick.ac.uk>
- Date: Fri, 11 Dec 1992 22:35:07 GMT
- Lines: 29
-
- 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.
-