386DX-33 -> DX-40 help \ VOGONS

386DX-33 -> DX-40 help

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First post, by McBierle

Posted on 2018-04-02, 14:49

McBierle Offline

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Hello again!

Next Questions:
I have this 386-board and identified it as "Unidentified 386 CACHE MAINBOARD" http://www.uncreativelabs.de/th99/m/U-Z/32256.htm.
DX-33 works as it should. When i put in an Am386-DX40 it clocks at 33Mhz. As you can see JP24-26 are not there and the oscillator shows 66Mhz.
Do you think it is possible to put in 80Mhz oscillator and connect the jumper points as 40mhz, or is there more to do?
And why is JP26 not closed?

Any help/ideas?

Thanks!

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Reply 1 of 5, by cyclone3d

Posted on 2018-04-02, 14:53

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Just replacing the oscillator with an 80Mhz one should do the trick.

For that matter, you really shouldn't even need to replace the 33Mhz CPU with the 40Mhz one as the 33Mhz one should run just fine at 40Mhz.

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Reply 2 of 5, by lazibayer

Posted on 2018-04-02, 15:21

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I had a 386 board that uses a clock generator chip, instead of a crystal, to produce 66 or 80MHz frequencies with respect to the jumpers' input. I guess the jumpers on your board are reserved for its chip-variant.

Reply 3 of 5, by gdjacobs

Posted on 2018-04-02, 16:00

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I'd actually love a programmable clockgen for testing underclocking on my 386DX40. I'm kind-of curious how low it can go.

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Reply 4 of 5, by Jo22

Posted on 2018-04-02, 20:55

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Me, too. AMD used a "static" CMOS design for its 80386 chips. Not sure about Intel, though.

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Reply 5 of 5, by McBierle

Posted on 2018-04-11, 18:10

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Hi guys,

it worked, many thanks! 😀

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