Siemens SIMATIC S7-1500 Function Manual page 311

Connection resources
11.1 Connection resources of a station
Reserved connection resources
10 connection resources are reserved for stations with S7-1500 CPU, ET 200SP CPU and
ET 200pro CPU based on S7-1500:
● 4 for PG communication required by STEP 7, for example, for test and diagnostics
functions or downloading to the CPU
● 4 for HMI communication which are occupied by the first HMI connections configured in
STEP 7
● 2 for communication with the Web server
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Function Manual, 11/2019, A5E03735815-AH
Communication