Functions And Operation Examples Of File Registers - Mitsubishi Electric MELSEC FX3U Programming Manual

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
4.9.4

Functions and operation examples of file registers

A file register is a device for setting the initial value of a data register with the same number.
Each file register stores 16-bit data (whose most significant bit specifies the positive or negative sign). Two
file registers combined can store 32-bit numeric data (whose most significant bit specifies the positive or
negative sign).
Up to 7000 data registers starting from D1000 can be specified as file registers by the parameter setting.
• In parameter settings, 1 to 14 blocks can be specified. One block secures 500 file registers, but uses the
program memory area by 500 steps.
• When some of data registers starting from D1000 are specified as file registers, the remaining data
registers not specified as file registers can be used as data registers.
This section explains how to handle file registers.
1. Operation of file registers
• The contents of the file register area [A] set inside the built-in memory or memory cassette are batch-
transferred to the data memory area [B] inside the system RAM when the power of the PLC is turned ON or
when the PLC mode switches from STOP to RUN.
When data registers are specified as file registers by the parameter setting, the contents of the file register
area [A] inside the program memory are transferred when the power of the PLC is turned ON or when the
PLC mode switches from STOP to RUN. This means that the contents changed in the data memory are
initialized every time when the PLC turns ON or when the PLC mode switches from STOP to RUN.
When it is necessary to save data changed in the data memory using a sequence program, update the file
register area [A] to the changed values by the same-number register update mode in BMOV
(FNC 15) instruction described later.
Inside built-in memory
memory cassette
D1000
500 points ×
14 blocks
maximum
(7000 points
maximum)
• Difference between BMOV (FNC 15) instruction and other instructions
The table below shows the differences between the BMOV (FNC 15) instruction and other applied
instructions.
Instruction
BMOV
instruction
Applied
instructions
other than
BMOV
instruction
The data stored in data registers set as file registers are automatically copied from the file register area [A]
to the data register area [B] when restoring the power.
or
Program
memory
When power
is turned ON
Program/
When PLC
comment
mode is
changed D1000
from STOP
File register
to RUN
[A]
D7999
The remaining area can be used as data registers for general purpose.
Transferred contents
Data can be read from and written to the file
register area [A] inside the program memory.
Data can be read from and written to the data
register area [B] inside the image memory in
the same way as general data registers.
Inside system
RAM
D 0
Data
memory
Data register
For devices D1000 and later specified
as operands in applied instructions other
than BMOV (FNC 15) , indirectly
Write
Data register
specified values for timers, counters or
[B]
devices in RST instructions can be read
from and written to the data register
Read
area [B] in the same way as general
Data register
data registers.
Because the data register area [B] is provided
inside the system RAM in the PLC, its contents can
be arbitrarily changed without being limited by the
optional memory format.
4 Devices in Detail
4.9 Data Register and File Register [D]
Remarks
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