FB_CheckWatchdog
Monitoring of a watchdog signal, which is transferred with the function block FB_WriteWatchdog.
The device to be monitored regularly sends a variable counter value to the device that is to monitor the transmission. The function block FB_CheckWatchdog is used there to monitor the state of the counter. If this does not change within a specific period, the bWatchdog output is set to TRUE. If a value of 0 s is specified for tWatchdogTime, the bWatchdog signal is set to FALSE. The period specified by tWachtdogTime should be a multiple (5-10 times) of the time in which the monitoring signal is transmitted.
VAR_INPUT
VAR_INPUT
bEnable : BOOL := FALSE;
tWatchdogTime : TIME := t#0s;
nCnt : UDINT;
END_VAR
bEnable: Enable function block.
tWatchdogTime: Duration during which nCnt has to change.
nCnt: Current counter value of the watchdog signal.
VAR_OUTPUT
VAR_OUTPUT
bWatchdog : BOOL := FALSE;
nLastCnt : UDINT;
END_VAR
bWatchdog: FALSE indicates a valid monitoring signal. The output will become TRUE if no change is detected in nCnt during the period of time specified by tWatchdogTime.
nLastCnt: Most recent successfully transmitted counter state of the monitoring signal.
Requirements
Development environment | required TC3 PLC library |
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TwinCAT v3.0.0 | Tc2_DataExchange |