Mitsubishi Electric MELSEC FX3U Programming Manual page 771

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
Guideline of the watchdog timer set value
A value acquired by the following procedure can be regarded as the guideline of the watchdog timer set
value.
If an acquired value is 200 ms or less, however, it is not necessary to change the watchdog timer set value.
1) Write a program to be executed from GX Developer to the PLC.
[Online]→[Write to PLC...]
2) Set the current value of D8000 (unit: ms) to "1000" using the device test function in GX Developer.
[Online]→[Debug]→[Device test...]→ "Word device/buffer memory" in Device test dialogbox
3) Set the PLC mode to RUN, and execute the program. (Execute this instruction also.)
4) Monitor the maximum scan time D8012 (unit: 0.1ms) using the device batch monitoring function in GX
Developer.
5) Set the watchdog timer to the maximum scan time (D8012) or more.
D8012 stores the maximum scan time in increments of 0.1 ms.
Rough guide to the watchdog timer set value D8000 (unit: ms) is the "value stored in D8012 divided by
10" added by 50 to 100.
• Setting WDT (FNC 07) instruction just before and after INITR instruction as shown below:
Command
input
If the processing time of the INITR command exceeds 200ms, set the watchdog timer value D8000 (unit: ms)
to the proceessing time or more.
2. Allowable number of writes to the memory
Note the following cautions on access to extension file registers.
• Data can be written to the memory cassette (flash memory) up to 10,000 times.
Every time the INITR (FNC292), RWER (FNC294) or INITER (FNC295) instruction is executed, it is
counted as a write to the memory. Make sure not to exceed the allowable number of writes.
When a continuous operation type instruction is used, data is written to the memory in every operation
cycle of the PLC. For preventing this, make sure to use a pulse operation type instruction.
• Execution of the LOADR (FNC290), SAVER (FNC291) or LOGR (FNC293) instruction is not counted as a
write to the memory. However, it is necessary to initialize the writing target sector before executing the
SAVER (FNC291) or LOGR (FNC293) instruction.
Every time the INITR (FNC292)or INITER (FNC295) instruction is executed, it is counted as a write to the
memory. Make sure not to exceed the allowable number of writes.
Errors
An operation error is caused in the following cases; The error flag M8067 turns ON, and the error code is
stored in D8067.
• When any device number other than the head device number of a sector of extension file registers is set to
(error code: K6706)
S
• When a device number to be initialized exceeds "32767" (error code: K6706)
In this case, devices up to R32767 (ER32767) are initialized.
• When the protect switch of the memory cassette is set to ON (error code: K6770)
FNC 07
WDT
FNC292
S n
INITR
FNC 07
WDT
33 Extension File Register Control – FNC290 to FNC299
33.3 FNC292 – INITR / Initialize R and ER
The watchdog timer is reset.
The watchdog timer is reset.
31
32
33
34
35
36
37
38
A
B
769