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Special instructions
F142_WDT
The scan 'check watchdog timer' is preset with the constant specified by s* if the trigger EN is in
Description
the ON-state. The value specified by s* is 1 to 255 and the preset time becomes 2.5 ms * s* (637.5
ms).
The scan 'check watchdog timer' is automatically set at the start of a scan with the value of the
system register (No. 30). To monitor the transit of a processing block, set the watchdog timer with
this instruction immediately before transition and set again immediately after that.
This instruction also exists as a P instruction (for FP2/2SH, FP3/5, FP10/10SH PLC types), which
is only executed at the rising edge of the EN trigger. Select [Insert P instruction] from the
"Instructions" pane if you require a P instruction. To facilitate reuse, the instruction then appears
under "Recently used" in the pop-up menu. Press <Ctrl>+<Shift>+<v> within the programming
area to open the list of recently used elements.
Availability of F142_WDT (see page 1321)
PLC types
Data types
Variable
Data type
INT
s
In this example the function has been programmed in ladder diagram (LD) and structured text
Example
(ST).The same POU header is used for all programming languages.
POU header
All input and output variables used for programming this function have been declared in the POU
header.
Body
When the variable start is set to TRUE, the function is carried out.
LD
ST
When programming with structured text, enter the following:
IF
start
THEN
(* Watchdog timer value is changed to 123.4ms *)
F142_WDT(1234);
END_IF;
1000
Watchdog timer update
Function
specifies watchdog timer value
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