Contec SPI-8550-LLVAS, User Manual

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5. CPU Board Resources
42
SPI-8550-LLVAS
Watch-Dog-Timer (WDT) Setting
The watchdog timer serves as a safeguard against possible system lock-up in your industrial computer
system. In most industrial environments, there are heavy equipment, generators, high-voltage power
lines, or power drops that have adverse effects on your computer system. For instance, when a power
drop occurs, it could cause the CPU to come to a halt state or enter into an infinite loop, resulting in a
system lock-up.
With the watchdog timer enabled, a RESET can be automatically generated unless the CPU periodically
triggers the timer within the time-out interval. That is, while the system gets hung up, the running
program can’t trigger the timer periodically. The timer will generate a reset signal to reboot the system.
This feature allows a running program to restart in an orderly way when a power glitch or any abnormal
condition occurs.
The watchdog timer comes with 255-level time-out interval, 1 to 255 seconds per interval, which can be
adjusted by software setting. There is a tolerance of 2 second for this time-out interval. For example, if
the time-out interval has been set to 32 seconds, your program should trigger the watchdog timer before
28 seconds are escaped. Otherwise, after 28-32 seconds are escaped, the system will automatically reboot.
To keep the system running normally, your program should trigger the watchdog timer every 28 seconds.
The I/O port is defined at address 2eH. You can trigger/enable disable the timer by writing port2e.
Here is a example for programming Watch dog timeout in "debug" mode.
Start WDT
o 2e 87
o 2e 87
o 2e 2b
o 2f 0d (setting multiplexed pin to be WDTO function)
o 2e 07
o 2f 08
o 2e 30
o 2f 01
o 2e f5
o 2f 00 (00:unit for second)
o 2e f6
o 2f xx ( any value by user select)
o 2e f7
i 2f
(bit4=1:detect time up of WDT =0:run WDT)
Stop WDT
o 2e f6
o 2f 00
o 2e f7
o 2f 00
CAUTION
The timer’s intervals have a tolerance of ± 2 seconds.