Re-Trigger Scan Cycle Watchdog Instruction - Siemens SIMATIC S7 System Manual

Sample steps for using the RET instruction inside an FC code block:
1. Create a new project and add an FC:
2. Edit the FC:
3. Call the FC from MAIN [OB1].
The EN input on the FC box in the MAIN code block must be true to begin execution of the
FC.
The value specified by the RET instruction in the FC will be present on the ENO output of the
FC box in the MAIN code block following execution of the FC for which power flow to the
RET instruction is true.
7.8.15

Re-trigger scan cycle watchdog instruction

Table 7- 116 RE_TRIGR instruction
LAD / FBD SCL
RE_TRIGR();
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.
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05
– Add instructions from the instruction tree.
– Add a RET instruction, including one of the following for the "Return_Value"
parameter:
TRUE, FALSE, or a memory location that specifies the required return value.
– Add more instructions.
Description
RE_TRIGR (Re-trigger scan time watchdog) is used to extend the maximum
time allowed before the scan cycle watchdog timer generates an error.
100BBasic instructions
7.8 Program control
221