Mitsubishi MELSEC-A Series Reference Manual page 160

7. DATA LINK SETTINGS
(2)
2) The system uses the M
Consider the range used by the system when assigning the M
[Number of points used by the system]
The link register (W) 1 point is used for one special function module installed
to a remote I/O station.
[Range used by the system]
The range used by the system begins at the M
number assigned to each remote I/O station to "number of use points -1 ".
Example
When three special function modules are installed to remote I/O station No.2 with
link parameters set as shown below, W360 to 362 in the M
are used by the system.
The device range that can be assigned to the second half link parameters is the
range assigned to the first half link parameters: "(final device number ) + 1 " or later.
(Example: If the range of B0 to FF is assigned to the first link parameters, "B100" or
later can be assigned to the second half parameters.)
If 0 point is assigned to the first half link parameters, assignment of the second half
link parameters can be started with W000.
POINT
(1) When only the RFRP instruction is used, set the M
system in the link parameter.
(2) If the M R area used by the system is used incorrectly in a user program,
data cannot be read/written correctly, when the RFRP/RTOP instruction is
executed.
R area to execute RFRP/RTOP instructions.
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R area.
R area head device
R area (W360 to 3AF)
R area used by the