Fnc 07 - Wdt / Watchdog Timer Refresh - Mitsubishi Electric FX3G SERIES Programming Manual

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
8.8 FNC 07 – WDT / Watchdog Timer Refresh
Outline
This instruction refreshes the watchdog timer in a sequence program.
1. Instruction format
FNC 07
WDT
2. Set data
Operand type
–
3. Applicable devices
Bit Devices
Oper-
and System User
Type
X Y M T C S D .b KnX KnY KnM KnS T C D R U \G
–
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.
Command
input
FNC 07
WDTP
Command
input
FNC 07
WDT
Related device
Device
D8000 Watchdog timer time
Cautions
1. When a watchdog timer error occurs
A watchdog timer error may occur in the following cases. To avoid the error, input a program shown below near the
head step to extend the watchdog timer time, or shift FROM/TO instruction execution timing.
1) Caution when many special extension devices are connected
In such configuration that many special extension devices (such as positioning units, cam switches, analog units
and link units) are connected, the buffer memory initialization time may become longer, thus the operation time
may become longer, and a watchdog timer error may occur.
2) Caution when many FROM/TO instructions are driven at one time
When many FROM/TO instructions are executed or when many buffer memories are transferred, the scan time
may become longer, and a watchdog timer error may occur.
3) Caution when there are many high-speed counters (software counters)
When many high-speed counters are provided and high frequency are counted at one time, the operation time
may become longer, and a watchdog timer error may occur.
238
Mnemonic
Independent Inst.
P
WDT
1 step
WDTP
There is no set data.
Digit Specification
Command
contact
Command
contact
Name
Up to 32767 ms can be set in units of ms (initial value: 200 ms).
8.8 FNC 07 – WDT / Watchdog Timer Refresh
Operation Condition
Continuous
Operation
Pulse (Single)
Operation
Description
Word Devices
Special
System User
Unit
V
There are no applicable devices.
One scan is executed.
Each scan is
executed.
Description
8 Program Flow – FNC 00 to FNC 09
Data type
Others
Con- Real Charac-
Index
stant Number ter String
Z Modify K H E " "
–
Pointer
P