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System Introduction 1-27
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 turns the power on/off for the hard
disk only.
2. HDD reset [pinW14(PX3_HDRST#) of PIIX4]. This pin provides the reset to the drive
when the drive is newly powered up. The reset pin is asserted when the drive is first
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. This pin is shared as a power on/off 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.