Справочник Пользователя для Mitsubishi Electronics FX
FX Series Programmable Controlers
Applied Instructions 5
5-12
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
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.
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. FX users have the additional option of using the pulse (P) format of
the WDT instruction, i.e. WDTP.
To force the WDT instruction to operate for only ONE scan requires the user to program
some form of interlock. FX users have the additional option of using the pulse (P) format of
the WDT instruction, i.e. WDTP.
b) The watchdog timer has a default setting of 100
msec for FX PLC’s and 200 msec for FX
0
/FX
0N
/
FX
2N
PLC’s. This time limit may be customized to
a users own requirement by editing the contents of
data register D8000, the watchdog timer register.
data register D8000, the watchdog timer register.
Mnemonic
Function
Operands
Program steps
D
WDT
FNC 07
(Watch dog
timer refresh)
FNC 07
(Watch dog
timer refresh)
Used to refresh
the watch dog
timer during a
program scan
the watch dog
timer during a
program scan
N/A
Can be driven at any time within the main
program body
Can be driven at any time within the main
program body
WDT, WDTP:
1 step
1 step
FX
0(S)
FX
0N
FX FX
(2C)
FX
2N(C)
FX
(2C)
FX
FX
2N(C)
FX
0N
FX
0(s)
PULSE-P
FX
(2C)
FX
FX
2N(C)
FX
0N
FX
0(s)
16 BIT OPERATION
FX
FX
0N
FX
0(s)
FX
(2C)
FX
2N(C)
32 BIT OPERATION
X0
WDT
END
END
WDT
Main program
Main program pt1
Main program pt2
Program scan
time 120 msec
time 120 msec
Program(pt2) scan
time 60 msec
time 60 msec
Program(pt1) scan
time 60 msec
time 60 msec
X0
WDTP
X0
WDT
X0
Excuted every program scan
FX only
All PCs general
operation
operation
Excuted in the
first program scan
first program scan
M8000
MOV K150 D8000