Topologies Between The Communication Partners; Figure 2-8 Rs 422 Point-To-Point; Figure 2-9 Rs 485 Point-To-Point - Siemens SIMATIC S7-400 CP 440 Installation And Parameter Assignment

Basic Principles of Serial Data Transmission
2.4 Data Transmission with the ASCII Driver
2.4.4

Topologies Between the Communication Partners

Applications
The CP 440 can be used in different topologies in the RS422 and RS485 operating modes.
Distinctions are drawn between connections with:
● Two nodes (point-to-point) and
● Several nodes (multipoint)
In these cases the CP 440 can be used as:
● Master or
● Slave
Figure 2-8
Figure 2-9
In the case of a master/slave topology, there must be an appropriate message frame in the
user program. Example: The master sends all the slaves a message frame with address
information. All the slaves listen in and compare the address with their own. If the address is
the same, the addressed slave sends its answer.
The senders of all slaves must be able to switch to low impedance.
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RS 422 Point-to-Point
RS 485 Point-to-Point
Point-to-point connection CP 440 Installation and Parameter Assignment
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Manual, 09/2007, A5E00057742-03