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MITSUBISHI ELECTRIC MOTHERBOARD DIVISION PAGE 22 OF 45
The motherboard supports an ACPI-compliant standby switch for use with a soft-switch power
supply. The action of the switch is under a combination of hardware and software control and is
summarised in the table below. The motherboard will power off regardless of the state of
software if the switch is held down for more than 4 seconds.
Standby (soft power off)
Machine powers up and executes POST
POST, DOS or APM O/S
Machine powers off into standby state
The ‘Wake on AC connect’ BIOS option and the state of the lithium cell determine the
behaviour of the motherboard after an AC-disconnect. The table below describes this.
CMOS RAM cleared. This is the state of a
new motherboard before assembly. This also
occurs after battery removal or failure.
Motherboard waits for standby switch
to be pressed.
CMOS RAM not cleared and ‘Wake on AC
connect’ was set to ‘Enabled’.
Motherboard fully powers up without
intervention.
CMOS RAM not cleared and ‘Wake on AC
connect’ was set to ‘Disabled’. This is the
default state. Resume events will be lost if an
AC power failure occurs.
Motherboard waits for standby switch
to be pressed.
Indication of the power state is via the power LED. When a standard LED is fitted, it is
illuminated when power (main 5V) is on. Three states can be indicated by using a two-colour
LED which is biased in the reverse direction to indicate a sleeping state. The table below
assumes the use of a yellow/green bi-colour LED with the green anode connected to the LED+
pin.
Power off
Off
Normal operation
Green
Sleeping
Yellow