Mitsubishi FX1N Series Programming Manual

FX Series Programmable Controlers Applied Instructions 5
5-13
5.1.6 WDT (FNC 07)
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
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.
Mnemonic Function
Operands
Program steps
D
WDT
FNC 07
(Watch dog
timer refresh)
Used to refresh
the watch dog
timer during a
program scan
N/A
Canbedrivenatanytimewithinthemain
program body
WDT, WDTP:
1step
FX 1S
FX1N FX2N
FX2NC
PULSE-P 16 BIT OPERATION 32 BIT OPERATION
X0
WDT
END
END
WDT
Main program
Main program pt1
Main program pt2
Program scan
time 120 msec
Program(pt2) scan
time 60 msec
Program(pt1) scan
time 60 msec
M8000
MOV K150 D8000

Mitsubishi FX1N Series Specifications

General

Programming Language	Ladder Logic
Output Type	Relay, Transistor
Operating Temperature	0 to 55°C
Power Supply	100-240V AC or 24V DC
Program Capacity	8K steps
Communication Ports	RS-422
Data Memory	8000 words
High-speed Counters	Up to 6 channels
Expansion Modules	Available
Pulse Output	2 points