Why can't HMI panels of botu V17 and below connect with CPUs of 1500 firmware version 2.9 or 1200 firmware version 4.5?

Why botu V17 And the following HMI The panel cannot be connected with 1500 Firmware version 2.9 or 1200 edition 4.5 Of CPU Establishing a connection ？

If you have S7-1500 CPU Firmware upgrade to 2.9 Version or S7-1200 CPU The firmware version is upgraded to 4.5, Now I want to V17 And the following panels (Basic, Comfort perhaps Unified) or RT Advanced Project communication .

When to start RT when , You will only get news “ Connection is broken ”.

TIA Portal V17 And above , And V4.5/V2.9 And above firmware version S7-1200/S7-1500 CPU perhaps 21.9 The soft controller communication of firmware version and above is automatically set to “ Security ” signal communication . This means that the connection partners automatically set their connection mechanism to the highest possible security process .

terms of settlement ：

For version < V17 Of HMI Be able to communicate with these controllers , stay “ Protection and safety > Connection mechanism ” Under the CPU Setting up , Must be disabled “ Only allow safe PG/PC and HMI signal communication ” function .

As shown in the figure below ,

When these changes are reloaded on the controller , That is, after downloading the configuration again , Can re-establish CPU and HMI Connection between .