Siemens SIMATIC NET CP 243-1 Technical Manual page 52

Configuration
Free connections
A free connection can only be used if your S7-300 or S7-400 system is to be oper-
ated as a server. Free connections do not have to configured in STEP 7. Standard
S7-300 and S7-400 systems are set up to communicate via free connections.
If you would like to make use of the mechanism for free connections in your S7-
300 or S7-400 system, the client side for each of these connections must still be
configured. In STEP 7 Micro/WIN 32, there is not difference between use of these
connections and communicating via connections that were configured in the S7-
300 or S7-400 system. For free connections, you must merely ensure that the first
byte of the TSAP over which these connections pass to the S7-300 and S7-400
systems is always assigned a value of 0x03. The second byte of the TSAP is de-
rived, as described above, from the rack and slot number of the CPU used in your
S7-300 or S7-400 system.
Note
S7-200 systems do not support free connections. This means that you must con-
figure each connection in an S7-200 system, regardless of whether your system is
to be operated as a client or server.
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09/02
CP 243-1
J31069-D0428-U001-A1-7618