Wdt (Fnc 07) - Mitsubishi FX1S Series Programming Manual

FX Series Programmable Controlers
5.1.6

WDT (FNC 07)

Mnemonic
WDT
FNC 07
(Watch dog
timer refresh)
16 BIT OPERATION
there is an error at some point. The PLC will then cease operation to prevent any further errors
from occurring. By causing the watchdog timer to refresh (driving the WDT instruction) the
usable scan (program operation) time is effectively increased.
Points to note:
a) When the WDT instruction is used it will operate on every program scan so long as its input
condition has been made.
To force the WDT instruction to operate for only ONE scan requires the user to program
some form of interlock.
b) The watchdog timer has a default setting of 200
msec. This time limit may be customized to a
users own requirement by editing the contents of
data register D8000, the watchdog timer register.
Function
Used to refresh N/A
the watch dog Can be driven at any time within the main
timer during a program body
program scan
32 BIT OPERATION
Operands
D
PULSE-P
Operation:
The WDT instruction refreshes the PLC's watchdog
timer. The watchdog timer checks that the program
scan (operation) time does not exceed an arbitrary time
limit. It is assumed that if this time limit is exceeded
Applied Instructions 5
FX FX FX
1S 1N 2N
Program steps
WDT, WDTP:
1 step
5-13
FX
2NC