Basic instructions
7.8 Program control operations
S7-1200 Programmable controller
262 System Manual, 03/2014, A5E02486680-AG
RE_TRIGR (Restart cycle monitoring time) instruction
Table 7- 104 RE_TRIGR instruction
RE_TRIGR (Re-trigger scan time watchdog) is used to extend the maximum
time allowed before the scan cycle watchdog timer generates an error.
Use the RE_TRIGR instruction to restart the scan cycle monitoring timer during a single scan
cycle. This has the effect of extending the allowed maximum scan cycle time by one
maximum cycle time period, from the last execution of the RE_TRIGR function.
-1200 CPU firmware version 2.2, RE_TRIGR was restricted to execution from a
ram cycle OB and could be used to extend the PLC scan time indefinitely. ENO =
FALSE and the watchdog timer is not reset when RE_TRIGR was executed from a start up
OB, an interrupt OB, or an error OB.
For firmware version 2.2 and later, RE_TRIGR can be exe
cuted from any OB (including start
up, interrupt, and error OBs). However, the PLC scan can only be extended by a maximum
of 10x the configured maximum cycle time.
Setting the PLC maximum cycle time
Configure the value for maximum scan cycle time in the Device configuration for "Cycle
time".
Table 7- 105 Cycle time values
If the maximum scan cycle timer expires before the scan cycle has been completed, an error
is generated. If the user program includes a time error interrupt OB (OB 80), the CPU
executes the time error interrupt OB, which can include program logic to create a special
reaction.
If the user program does not include a time error interrupt OB, the first timeout condition is
ignored and the CPU remains in RUN mode. If a second maximum scan time timeout occurs
in the same program scan (2 times the maximum cycle time value), then an error is triggered
that causes a transition to STOP mode.
In STOP mode, your program execution stops while CPU system communications and
system diagnostics continue.
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