Applies To:
  • CitectSCADA 5.xx
  • CitectHMI 5.xx

Citect S7 drivers use the Siemens Softnet S7 API to connect to the Siemens S7 PLCs.The Siemens S7-300 PLCs normally allow only 2 S7 connections from external applications. How can I get more S7 connections to the S7-300 PLCs for Citect to use? 

The limit of 2 S7 connections is a limitation in the Siemens CPU module. With the newer S7-300 CPUs (eg. 315-2DP with P/N 6ES7 315-2AG10-0AB0 V2 firmware), the CPU allow a maximum of 16 S7 connections. However, 2 S7 connections are reserved for the Siemens OP and PG, 2 are reserved for external applications and with the remaining 12 connections reserved for "Siemens S7 connections". Thus to get more S7 connections for Citect to use, you will need to reduce the reserved "Siemens S7 connections".

To do this, go to the Hardware Configuration, Select the CPU module and choose "Properties". Go to the "Communication" tab. The "S7 Standard Communication" setting should have a default value of 12. Reduce this number to increase the external S7 connections required for Citect to use. For example, reducing the "S7 Standard Communication" from 12 to 8 will allow 6 external S7 connections for Citect to use.