32
•
Fieldbus coupler 750-342
Data exchange
Modular I/O System
ETHERNET TCP/IP
3.1.5.1 Memory
areas
I
O
memory area
for input data
I/O modules
input
modules
word 255
output
modules
word 0
word 255
fieldbus
master
word 0
memory area
for output data
fieldbus coupler
1
2
Fig. 3-9: Memory areas and data exchange for a fieldbus coupler
g012939e
The coupler process image contains the physical data of the bus modules in a
storage area for input data and in a storage area for output data (word 0 ... 255
each).
(1) The input module data can be read from the fieldbus side.
(2) In the same manner, writing on the output modules is possible from the
fieldbus side.
In addition, all output data of the ETHERNET TCP/IP coupler are mirror im-
aged on a storage area with the address offset 0x0200. This allows to read out-
put values back by adding 0x0200 to the MODBUS address.
3.1.5.2 Addressing
3.1.5.2.1 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 or-
der 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.
