Siemens SIMATIC S7-1500 Function Manual page 316

Monitoring the maximum possible number of connection resources
Offline
During configuration of connections, STEP 7 monitors the occupation of the connection
resources. If the maximum possible number of connection resources is exceeded, STEP 7
signals this with a suitable warning.
Online
The CPU monitors the use of connection resources in the automation system. If you
establish more connections in the user program than those provided by the automation
system, the CPU acknowledges the instruction to establish the connection with an error.
S7-1500 and S7-300 comparison
You will find a comparison of how the communication resources of the S7-1500 and S7-300
are managed in this FAQ (https://support.industry.siemens.com/cs/ww/en/view/109747092).
Communication
Function Manual, 11/2019, A5E03735815-AH
Connection resources
11.2 Allocation of connection resources
315