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More Advanced Programming
5.2.5
Exchanging data with special function modules
You can add expansion modules to increase the number of inputs and outputs available to all
base units of the MELSEC FX series except the FX
you can also supplement the controller's functions by adding so-called "special function mod-
ules" – for example for reading analog signals for currents and voltages, for controlling temper-
atures and for communicating with external equipment.
The digital I/O expansion modules do not require special instructions; the additional inputs and
outputs are handled in exactly the same way as those in the base unit. Communication
between the base unit and special function modules is performed with two special applied
instructions: the FROM and TO instructions.
Each special function module has a memory range assigned as a buffer for temporary storage
of data, such as analog measurement values or received data. The base unit can access this
buffer and both read the stored values from it and write new values to it, which the module can
then process (settings for the module's functions, data for transmission etc).
The buffer memory can have up to 32,767 indi-
vidual addressable memory cells, each of
which can store 16 bits of data. The functions of
the buffer memory cells depends on the indi-
vidual special function module – see the mod-
ule's documentation for details.
The following information is required when you use the FROM and TO instructions:
–
The special function module to be read from or written to
–
The address of the first buffer memory cell to be read from or written to
–
The number of buffer memory cells to be read from or written to
–
The location in the base unit where the data from the module is to be stored or containing
the data to be written to the module
FX Beginners Manual
Base unit
Device memory
Instructions for Moving Data
and the FX
1S
3S
Special function module
Buffer memory
TO
FROM
Buffer memory address 0
Buffer memory address 1
Buffer memory address 2
Buffer memory address n-1
Buffer memory address n-1
models. In addition to this
:
:
5 – 13
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