1-26 Service Guide

Table 1-15 PMU Timers List

Item Descriptions
System activities
and timer retriggers System activities
Power off either or both FDD and CD-ROM. Tri-state FDD and CD-ROM
interfaces and stop IDE controller clock.
Timer retriggers
The I/O access to 3F2, 3F4, 3F5(FDD), 3F7, 376(CD ROM) will retrigger the
timer.
Detective hardware
change 1. The PX3_FDDBEN signal on pin-M3 of U21(PIIX4) is from L to H. CD-ROM
buffer is disabled.
2. The pin-T14(PX3_CD/FDPON) of U21(PIIX4) is from H to L, the FDD/CD-ROM is
powered off.
1.6.7.2 Component activities in power saving mode
Hard disk
The hard disk is fully power managed. This means that when the hard disk is not in use, the
hard disk is powered off. The following pins are dedicated toward the management of power
on the hard disk.
1.

HDD power enable pinY15(PX3_HDPON).

This pin tur ns the power on/of f f or the hard dis k
only.
2.

HDD reset [pinW14(PX3_HDRST#) of PIIX4].

This pin provides the r es et to the dr ive when
the drive is newly powered up. The reset pin is as ser ted when the drive is f irs t powered up,
then the reset is removed after the drive is powered up and before the interface is enabled.
CD-ROM
The CD-ROM and the hard disk are both IDE devices. They share the same controller. The
following pins are dedicated toward the management of power on the CD-ROM.
1.

CD-ROM buffer enable [pin-M3 of U21 PX3-FDDBEN of PIIX4].

The CD buffer enable
separates the CD-ROM from the IDE controller. This buffer must be disabled before the
CD-ROM is turned off. The buffer is re-enabled after the CD-ROM is turned on and
brought out of reset.
2.

CD-ROM power control [pin-T14 of U21(PX3_CD/FDPON) of PIIX4].

The power control pin
is used to turn the CD-ROM unit off or on. T his pin is shared as a power on/of f pin for the
floppy disk as well.

If either the internal or external floppy or the CD-ROM is active, then

this control pin must be asserted on.