> Best I can make out, to trigger power-on on an ATX motherboard,
> you need to pull to TTL low momentarily? Anyone vouch for this?

There's a pullup to Vstandby in the I/O controller. Grounding will
boot the computer.

In a recent magazine article someone suggested the following -

Adding a series 100R on PWRBTN# and a 470uF across the
switch (!!!!! NOTE this is NOT for PCs that have mains on the
power switch !!!!!!!) performs an auto-boot when mains is turned
on at the wall. It's like pulling /MCLR momentarily low on a PIC
when Vcc is applied

> Is decoupling or anything else required on this signal path? My
> goal is to control on/off of an ATX PC (and power supply) via a
> PIC and IR

I'd make sure that ONLY a long-ish stream of IR pulses or coded
signal can get through to the switch, otherwise any old Tom Dick
or Harry glitch coming out of the IR receiver will cycle the PC

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