WinSystems PCM-VDX-2-512, Product Manual

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140808 PRODUCT MANUAL PCM-VDX-2-512 17
Watchdog Timer
The PCM-VDX-2-512 features an advanced watchdog timer which can be used to guard against software lockups. Two
interfaces are provided to the watchdog timer. The Advanced interface is the most flexible and recommended for new
designs. The other interface option is provided for software compatibility with older WinSystems single board computers.
Advanced
The watchdog timer can be enabled in the BIOS Settings by entering a value for Watchdog Timeout on the Chipset →
SouthBridge Configuration screen. Once the operating system is loaded, the watchdog can be disabled or reconfigured in
the application software.
NOTE: It is recommended that a long timeout be used if the watchdog is enabled when trying to boot any operating
system.
The watchdog can be enabled, disabled or reset by writing the appropriate values to the configuration registers located
at I/O addresses 565h and 566h. The watchdog is enabled by writing a timeout value other than zero to the I/O address
566h and disabled by writing
00h to this I/O address. The watchdog timer is serviced by writing the desired timeout value
to I/O port 566h. If the watchdog has not been serviced within the allotted time, the circuit resets the CPU.
The timeout value can be set from 1 second to 255 minutes. If port 565h bit 7 equals 0 , the timeout value written into I/O
address 566h is in minutes. The timeout value written to address 566h is in seconds if port 565 bit 7 equals 1 .
Port Address Value Reset Interval
1EEH
00h DISABLED
01h 2 SECONDS
1EFH ANY RESET TIMER
Port Address Port Bit 7 Value Port Address Value Reset Interval
565H x 566H 00h DISABLED
565H 1 566H 03h 3 SECONDS
565H 1 566H 1Eh 30 SECONDS
565H 0 566H 04h 4 MINUTES
565H 0 566H 05h 5 MINUTES
Software watchdog timer PET = PORT 566H, write the timeout value.
Watchdog Timer Examples
Legacy
This interface is provided for legacy software support only and is not recommended for new development.
The watchdog can be enabled or disabled via software by writing an appropriate timeout value to I/O port 1EEH. See the
chart provided below.