Siemens SIMATIC S7 System Manual page 420

Communication
8.4 Ethernet
TSAPs
Using Transport Service Access Points (TSAPs), ISO-on-TCP protocol allows multiple
connections to a single IP address. TSAPs uniquely identify these communication end point
connections to an IP address.
The ISO-on-TCP protocol utilizes port 102 exclusively. You cannot set the port number for
this protocol; however, you can set the TSAP for the local and remote partner.
The TSAP rules are shown below:
● You always enter TSAPs as an S7-200 SMART string data type (a length byte followed
by the string characters).
● TSAPs must be at least 2 characters and no more than 16 ASCII characters in length.
● The local TSAP cannot start with string "SIMATIC-"
● The local TSAP must begin with the hexadecimal character "0xE0" if the TSAP is exactly
2 characters long. For example, the TSAP "$E0$01" is legal but the TSAP "$01$01" is not
legal. (The "$" character denotes that the following value is a hexadecimal character.)
420
System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART