Asus P5GC-MX - Manual (Page 34)

1-22 Chapter 1: Product introduction
The total current consumed must NOT exceed the power
supplycapability (+5VSB) whether under normal condition or in sleep
mode.
2. USB device wake-up (3-pin PS2_USBPWR)
This jumper allows you to enable or disable the keyboard wake-up
feature. Set this jumper to pins 2-3 (+5VSB) to wake up the computer
when you press a key on the keyboard (the default is the Space Bar).
This feature requires an ATX power supply that can supply at least
500 mA on the +5VSB lead, and a corresponding setting in the BIOS.
P5GC-MX R
P5GC-MX USB Device Wake Up
3 2 2 1
PS2_USBPWR
(Default)
+5V +5VSB