Communication
8.6 RS485
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
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8.6.1
PPI protocol
Definition
PPI is a master-slave protocol: the master devices send requests to the slave devices, and
the slave devices respond. See the following figure. Slave devices do not initiate messages,
but wait until a master sends them a request or polls them for a response.
Masters communicate to slaves by means of a shared connection which is managed by the
PPI protocol. PPI does not limit the number of masters that can communicate with any one
slave; however, you cannot install more than 32 masters on the network.
PPI protocol and S7-200 SMART CPUs
PPI Advanced allows network devices to establish a logical connection between the devices.
With PPI Advanced, there are a limited number of connections supplied by each device. See
the following table for the number of connections supported by the S7-200 SMART CPU.
All S7-200 SMART CPUs support both PPI and PPI Advanced protocols.
Table 8- 13 Number of connections for the S7-200 SMART CPU
Module
Baud rate
Connections
RS485 port
9.6 Kbps, 19.2 Kbps, or 187.5 Kbps
5
RS485/RS232 signal board
9.6 Kbps, 19.2 Kbps, or 187.5 Kbps
4
Note
The CPU models CPU CR20s, CPU CR30s, CPU CR40s, and CPU CR60s do not support
the use of expansion modules or signal boards.