Mitsubishi Electric MELSEC FX3U - FNC 07 - WDT; Watchdog Timer Refresh

246
FX3G/FX3U/FX3UC Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
8 Program Flow – FNC 00 to FNC 09
8.8 FNC 07 – WDT / Watchdog Timer Refresh
8.8 FNC 07 – WDT / Watchdog Timer Refresh
Outline
This instruction refreshes the watchdog timer in a sequence program.
1. Instruction format
2. Set data
3. Applicable devices
Explanation of function and operation
When the operation cycle (time until END or FEND instruction is executed after the step 0) of a PLC exceeds
200 ms, a watchdog timer error (indicating abnormal operation) occurs; The CPU error LED lights, and the
PLC stops.
When the operation cycle is long, insert WDT instruction in the middle of the program to avoid the watchdog
timer error.
Related device
Operand type Description Data type
– There is no set data. –
Oper-
and
Type
Bit Devices Word Devices Others
System User Digit Specification System User
Special
Unit
Index
Con-
stant
Real
Number
Charac-
ter String
Pointer
XYMTCSD
 .b KnX KnY KnM KnS T C D R U  \G  VZModifyKH E "  "P
– There are no applicable devices.
Device Name Description
D8000 Watchdog timer time Up to 32767 ms can be set in units of ms (initial value: 200 ms).
P
FNC 07
WDT
WDT
Continuous
Operation
Pulse (Single)
Operation
Mnemonic Operation Condition
Independent Inst.
1 step
WDTP
FNC 07
WDTP
Command
input
One scan is executed.
Command
contact
Command
input
Each scan is
executed.
FNC 07
WDT
Command
contact