Communication
11.2 PROFINET
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
963
S7 routing between CPU and CP interfaces
Since the S7-1200 CPUs are limited to a single PN interface, a stand-alone CPU cannot
serve the function of a router. You can never connect a stand-alone CPU to more than one
S7 subnet at a time. When you install CP modules in the local base of the CPU, you can
connect to multiple S7 subnets and utilize routing.
In the example system below, in order for PLC_1 to communicate with PLC_3, the
Engineering System (ES) must rout messages through PLC_2. The ES must download the
routing table for PLC_2, and PLC_2 must provide the routing table for the CP module in its
local base. With these routing tables in place, PLC_1 and PLC_3 can communicate with
each other, even though not directly connected.
In order to check routing from either S7 subnet to the other S7 subnet, PLC_1 must establish
a transport connection to PLC_3, and PLC_3 must establish a connection to PLC_1. Doing
so, makes sure that routing from the PLC’s PN/IE interface to a CP module is possible as
well as routing from a CP module to the PLC’s PN/IE interface.
S7 routing between two CP interfaces
Since the S7-1200 CPUs support up to three CP modules, you can connect all three
modules to different S7 subnets. When you install at least two CP modules in the local base
of the CPU and connect to different S7 subnets, you can utilize routing.
In the example system below, in order for PLC_1 to communicate with PLC_3, the
Engineering System (ES) must rout messages by PLC_2 from the CP module to the CP
module in its local base. The ES must download the routing table for PLC_2, and PLC_2
must provide the routing table for the two CP modules. With these routing tables in place,
PLC_1 and PLC_3 can communicate with each other, even though not directly connected.
Also, you should note that routing takes place from CP module to CP module without
messages being sent over the PN/IE interface of PLC_2.
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