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User Guide XB1 COM Express Module
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Watchdog/Reset
The XB1 COM Express Module is provided with two supervisor circuits to monitor the supply voltages
1.8V, 3.3V, 5V, and to generate a clean power-on reset signal. The healthy state of the XB1 COM
Express Module immideately after a reset is signalled by the LED PG (Power Good), indicating that all
power voltages are within their specifications and the reset signal has been deasserted.
An important reliability feature is the watchdog function, which is programmable by software. The
behaviour of the watchdog is defined within the PLD, which activates/deactivates the watchdog and
controls its time-out period. The time-out delay is adjustable in the steps 2, 10, 50 and 255 seconds.
After alerting the WD and programming the time-out value, the related software (e.g. application
program) must trigger the watchdog periodically. All watchdog related functions are made available
by calling service requests within the BIOS.
The watchdog is in a passive state after a system reset. There is no need to trigger it at boot time. The
watchdog is activated on the first trigger request. If the duration between two trigger requests
exceeds the programmed period, the watchdog times out and a system reset will be generated. The
watchdog remains in its active state until the next system reset. There is no way to disable it once it
had been put on alert, whwereas it is possible to reprogram its time-out value at any time.
PG (Power Good) LED
The XB1 COM Express Module offers a software programmable LED located. After system reset, this
LED defaults to signal the board healthy respectively power good. By the first setting of the GPO20 of
the ICH6 this LED changes its function and is then controlled only by the level of the GPO20 pin.
Setting this pin to 1 will switch on the LED. The PG LED remains in the programmable state until the
next system reset.
GP (General Purpose) LED
A second, programmable LED can be also observed from the front panel. The status of the GP LED is
controlled by the GPO18 output of the ICH6. Setting this pin to 1 will switch on the LED. As of
current, the GP LED is not dedicated to any particular hardware or firmware function (this may change
in the future).