Siemens SIMATIC CP 440, Руководство пользователя

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Basic Principles of Serial Data Transmission
2-22
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02
Topologies Between the Communication Partners
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 RS 422 Point-to-Point
Figure 2-9 RS 485 Point-to-Point
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.
In the case of a master/slave topology in RS422 operation:
– The master’s sender is interconnected with the receivers of all the slaves.
– The slaves’ senders are interconnected with the master’s receiver.
– Only the receiver of the master and the receiver of one slave have a default
setting. All the other slaves function without default settings.