4
FUNCTIONS
4.12 Watchdog Timer (WDT)
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OVERVIEW
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SYSTEM
CONFIGURATION
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SPECIFICATIONS
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FUNCTIONS
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ACCESS VIA NETWORK
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PREPARATORY
PROCEDURES AND
SETTING
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I/O NUMBER
ASSIGNMENT
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MEMORIES AND FILES
4.12 Watchdog Timer (WDT)
(1) What is watchdog timer (WDT)?
Watchdog timers are provided inside the C Controller module to detect failure of the
hardware or user program.
The C Controller module has the following two different watchdog timers.
(a) System watchdog timer
The system watchdog timer monitors the system of the C Controller module, and
is used to detect a fault in the hardware or system software.
(b) User watchdog timer
The user watchdog timer monitors the user programs, and is used to detect an
error in the user programs.
(2) When a watchdog timer times out
When a watchdog timer times out, a watchdog timer error is detected and the
following conditions occur.
• The C Controller module turns off all the outputs.
• The RUN LED on the front of the C Controller module turns off, and the ERR.
LED flashes. (Only for a system watchdog timer error, the MODE LED also turns
off.)
(3) Setting and resetting a watchdog timer
(a) Setting a watchdog timer
1) System watchdog timer
Time for the system watchdog timer can be set or changed in <<System
settings>> of C Controller setting utility.
The default is 1000ms. (This can be changed within the range of 20ms to
2000ms (in 10ms units).)
2) User watchdog timer
Time for the user watchdog timer can be set by the QBF_StartWDT function
within the range of 100ms to 10000ms (in 10ms units).
(b) Resetting a watchdog timer
1) System watchdog timer
The system watchdog timer is periodically reset in the C Controller module.
If the system processing is interrupted for a long time due to a C Controller
module hardware error or an interrupt program execution, the system
watchdog timer can time out.
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