Fieldbus coupler 750-342 • 23
Process image
Modular I/O System
ETHERNET TCP/IP
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.
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 orien-
tated 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 proc-
ess 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 coupler provides a storage area of 256 words each (word 0 - 255) for the
physical input and output data.
Содержание I/O-SYSTEM 750
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