Program Control Instructions; Reset Scan Cycle Watchdog Instruction - Siemens SIMATIC S7 System Manual

Programming instructions
6.2 Extended instructions
occurrence of IN2 string is returned at OUT. If the string IN2 is not found in the string IN1,
then zero is returned. The following table shows the condition codes for the instruction.
ENO
1
0
6.2.4

Program control instructions

6.2.4.1

Reset scan cycle watchdog instruction

Use the RE_TRIGR instruction to restart the scan cycle 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.
The CPU restricts the use of the RE_TRIGR instruction to the program cycle, for example,
OB1 and functions that are called from the program cycle. This means that the watchdog
timer is reset, and ENO = EN, if RE_TRIGR is called from any OB of the program cycle OB
list.
ENO = FALSE and the watchdog timer is not reset if RE_TRIGR is executed from a start up
OB, an interrupt OB, or an error OB.
Setting the PLC maximum cycle time
You can set the value for maximum scan cycle time in the PLC device configuration for
"Cycle time".
Cycle time monitor
Maximum cycle time
Watchdog timeout
If the maximum scan cycle timer expires before the scan cycle has been completed, an error
is generated. If the error handling code block OB80 is included in the user program, the PLC
executes OB 80 where you may add program logic to create a special reaction. If OB80 is
not included, the first timeout condition is ignored.
If a second maximum scan time timeout occurs in the same program scan (2 times the
maximum cycle time value), an error is triggered that causes the PLC to transition to STOP
mode.
In STOP mode, your program execution stops while PLC system communications and
system diagnostics continue.
150
Condition
No errors detected
IN2 is larger than IN1
RE_TRIGR (Re-trigger scan time watchdog) is used to extend the
maximum time allowed before the scan cycle watchdog timer generates an
error.
Minimum value
1 ms
OUT
Valid character position
Character position is set to 0
Maximum value
6000 ms
S7-1200 Programmable controller
System Manual, 11/2009, A5E02486680-02
Default value
150 ms