Cautions On Using File Registers - Mitsubishi Electric MELSEC-Q Structured Programming Manual

FXCPU Structured Programming Manual
[Device & Common]
2.8.5

Cautions on using file registers

1. Cautions on using a memory cassette
When changing the contents of file registers secured in a memory cassette, satisfy the following conditions:
• Set to OFF the protect switch of the memory cassette.
• Allowable number of times of writing data to the program memory
When data is written by a continuous operation type instruction in a program, data is written to the program
memory in each operation cycle of the PLC.
For preventing this, make sure to use a pulse execution type instruction (BMOVP).
• Writing data to the flash memory
<In the case of FX
- It takes 66 to 132 ms to write data to one serial block (500 points).
Execution of the program is paused during this period. Because the watchdog timer is not refreshed
during this period, it is necessary to take proper countermeasures such as inserting the WDT instruction
into the sequence program.
- Do not turn OFF the power while the contents of file registers are changed.
If the power is turned OFF during the change, the data stored in file registers may be filled with
unexpected values, or a parameter error may occur.
• Writing data to the EEPROM memory
<In the case of FX
It takes 80 ms to write data to one serial block (500 points).
Execution of the program is paused during this period but the watchdog timer is refreshed automatically,
cautions are required.
<In the case of FX
It takes 10ms to write data to 1 point.
Execution of the program is paused during this period, and the watchdog timer is automatically refreshed.
<In the case of FX
Write data from peripheral equipment.
2. Cautions on handling file registers using the same-number register update function of the
BMOV instruction
• When updating the contents of file registers having the same number, make sure that the file register
number is same between the input variable
• Make sure that the number of transfer points specified by "n" does not exceed the file register area.
• If the number of transfer points exceeds the file register area, an operation error (M8067) occurs and the
BMOV instruction is not executed.
• Indexing
When the input variable
the actual device number is located within the file register area and if the number of transfer points does
not exceed the file register area.
→ For the allowable number of times of writing data, refer to Section 6.4.
/FX PLCs>
3U 3UC
/FX /FX PLCs>
3S 3G 3GC
/FX /FX /FX /FX
1S 1N 1NC 2N 2NC
PLCs>
0N
and output variable
2.8 Data Register and File Register [D]
PLCs>
and the output variable
are indexed, the BMOV instruction is executed if
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