Re: Multiple motherboards from a single PSU
- From: Frazer Jolly Goodfellow <no-spam@xxxxxxxxxxx>
- Date: Mon, 13 Feb 2006 01:07:36 GMT
scott.leckie@xxxxxxxxxxx wrote in
Hi, thanks for your response.
Ideally, I'd like one per motherboard but I'm not sure what will
happen when you signal PSON to ground, starting a shutdown, but
the power lines stay active (because the other mobos are still
On further reflection, the diodes in the PWR_OK connections are
redundant: once any one of the PS_ON#s is asserted (active low),
the PSU will assert PWR_OK (active high) and all 4 mobos will see
it, diodes or not.
Now comes the tricky bit. Under normal circumstances:
1) The power on button of an ATX PC provides a momentary low signal
to the motherboard.
2) The motherboard responds to that signal for its own purposes.
3) The motherboard then asserts PS_ON# to the PSU.
4) The PSU starts up and asserts PWR_OK.
In your 4-way independent power button scenario, the first mobo you
power up will see the right signals in sequence. But the other
three will all see PWR_OK go TRUE without having had a power on
momentary input. So the issue is: what does a mobo do in that
a) Do nothing until the power on button is pressed - the required
b) Power up and run normally - unlikely, and not the required
c) Power up in an undefined state and misbehave because step 2) was
missed out. *Definitely* not the required action.
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