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Detailed hardware description
Issue G
105
Watchdog timer
The APOLLO provides a Maxim MAX6369KA watchdog timer with a pin-selectable
timeout of 1ms to 60 seconds. This can be used to generate a complete hardware
system reset when an error causes a system lockup. By default, the watchdog timer is
disabled and once enabled must be triggered within the timeout period specified. The
table below lists the ICH4 GPIO connections relating to the watchdog timer, these ports
are configured as outputs by the BIOS during boot and are active during standby (S3).
The watchdog output has an open drain connection to the system reset line.
The ICH4 GPIO registers are accessed via an IO location mapped through the ICH4 LPC
interface bridge (Bus: 00h, Device: 1Fh, Function: 00h). Please refer to the Intel
82801DB ICH4 datasheet for additional information on the ICH4 GPIO and to the Maxim
MAX6369 datasheet for additional information on the watchdog timer settings.
ICH4 GPIO
Default Level
MAX6369KA
GPIO25 High
SET0
GPIO27 High
SET1
GPIO28 Low
SET2
GPIO24 Low
WDI
System control interface
A system control interface connector, J14, is provided to interface to standard input
switches and status indicators for:
•
System reset switch.
A connection for a momentary on reset switch. This provides standard PC reset
functionality.
•
Power button (on/off switch).
A connection for a momentary on ACPI power button. This provides standard PC
on/off functionality. The on/off switch ACPI functionality is configured in the BIOS
power management setup screen (see page
). Holding the on/off switch on for 5
seconds turns the ATX power supply off.
•
Tamper detection.
A connection for a normally open switch. The tamper detection circuitry is included in
the RTC circuitry (see the previous page for further details). A tamper is detected
when the switch contacts close.
•
PC speaker.
A connection to a standard 8
Ω
speaker to support PC speaker functionality. The PC
speaker output is also routed to the AC97 Codec and can be mixed with the audio
output.
•
HDD activity.
A connection for a hard drive activity LED. This LED shows activity on both the IDE
based devices and for the CompactFlash
®
socket.