101019
OPERATIONS MANUAL PPM-LX800-G
16
Watchdog Timer
The PPM-LX800-G features an advanced watchdog timer which can be used to guard
against software lockups. Three interfaces are provided to the watchdog timer. The
Advanced interface is the most flexible and recommended for new designs. The other
two interface options are 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 Watch-
Dog Timeout on the Peripherals screen. Any non-zero value represents the number of
minutes prior to reset during system boot. 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 256 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
3 SECONDS
03h
30 SECONDS
05h
300 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
Watchdog Timer Examples
Legacy
The Legacy watchdog timer has a fixed reset interval of 1.5 seconds. The watchdog
can be enabled by writing 1 or disabled by writing a 0 to I/O port address 1D0.
Standard
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.
Port Address
Value
Reset Interval
1D0
00h
DISABLED
01h
Enabled 1.5 sec
1D8H
ANY
RESET TIMER