Process Image - WAGO 750-341 Manual

42 • Fieldbus Coupler 750-341

Process image

3.1.4 Process image
After switching on, the coupler recognizes all I/O modules plugged into the
node which supply or wait for data (data width/bit width > 0).
The maximal length of a node is limited to 64 I/O modules.
Note
Use of the WAGO 750-628 Bus Extension Coupler Module and the 750-627
Extension End Module enables support of up to 255 I/O modules on the
750-341 coupler.
Note!
Expansion to 255 I/O modules is not enabled in the initial version of the
750-341 Fieldbus coupler.
Note
For the number of input and output bits or bytes of the individually activated
I/O modules, please refer to the corresponding I/O module description.
The coupler produces an internal process image from the data width and the
type of I/O module as well as the position of the I/O modules in the node. It is
divided into an input and an output data area.
The data of the digital I/O modules is bit orientated, i.e. the data exchange is
made bit for bit. The analog I/O modules are representative for all byte
orientated I/O modules, i.e. those where the data exchange is made byte for
byte. These I/O modules include for example the counter modules, I/O
modules for angle and path measurement as well as the communication
modules.
The data of the I/O modules is separate from the local input and output
process image in the sequence of their position after the coupler in the
individual process image.
First, all the byte oriented bus modules and then the bit oriented bus modules
are stored in the process image. The bits of the digital modules are grouped to
form bytes. As soon as the number of digital I/O's exceeds 8 bits, the coupler
automatically starts the next byte.
Note
A process image restructuring may result if a node is changed. In this case the
process data addresses also change in comparison with earlier ones. In the
event of adding modules, take the process data of all previous modules into
account.
The process image for physical input and output data is stored in the first 256
words of memory (word 0 to 255). This memory actually consists of a
separate area for the input and output data, but both areas are referenced in a
PLC program with an index of 0 to 255 for word operations.
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