Addressing The I/O Modules; Data Exchange Between Modbus Master And I/O Modules - WAGO 750-341 Manual

62 • Fieldbus Coupler 750-341
Data Exchange
3.1.5.2

Addressing the I/O modules

The arrangement of the I/O modules in a node is optional.
When addressing, first of all the more complex modules (modules occupying 1
or more bytes) are taken into account in accordance with their physical order
behind the fieldbus coupler. As such, they occupy the addresses starting with
word 0.
Following this, the data of the other modules (modules occupying less than 1
byte) follow, grouped into bytes. In accordance with the physical byte-wise
order this data is used to fill up the bytes. As soon as a full byte is occupied by
the bit-oriented modules, the next byte is automatically started.
Note
For the number of input and output bits and/or bytes of the individual activated
bus modules, please refer to the pertaining descriptions of the bus modules.
Note
Once a node is modified, a new architecture of the process image can result. As
such, the address of the process data will alsochange. In the event of adding
modules, the process data of all previous modules has to be taken into account.
Data width ≥ 1 Word / channel
Analog input modules
Analog output modules
Input modules for thermal elements
Input modules for resistance sensors
Pulse width output modules
Interface module
Up/down counter
I/O modules for angle and path measurement
Table 3.1.1: I/O module data width
3.1.5.3

Data exchange between MODBUS master and I/O modules

The data exchange between the MODBUS master and the I/O modules is made
by the implemented MODBUS functions in the coupler with reading and
writing in bits or bytes.
The coupler handles four different types of process data:
•
•
•
•
The word for word access to the digital input and output modules is made in
accordance with the following table:
Input words
Output words
Input bits
Output bits
Data width = 1 Bit / channel
Digital input modules
Digital output modules
Digital output modules with diagnosis (2 Bit / channel)
Power supply modules with fuse holder / diagnosis
Solid State power relay
Relay output modules
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