Process Image - WAGO 750 Series Manual

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). Analog and
digital I/O modules can be mixed on the same node.
Attention
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.
Attention
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 coupler provides a storage area of 256 words each (word 0 - 255) for the
physical input and output data.
Access from the fieldbus side is fieldbus specific. For the ETHERNET
TCP/IP fieldbus coupler, a MODBUS/TCP master accesses the data via
implemented MODBUS functions. Here decimal and/or hexadecimal
MODBUS addresses are used.
More information
A detailed description of these fieldbus-specific data access operations is
given in the section "MODBUS functions".
More Information
You can find the fieldbus specific process data architecture for all I/O
Modules in the chapter „Fieldbus specific Process Data Architecture".
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
Fieldbus coupler 750-342 • 45
Process image