Hi
What is No-Dp mode ?
can s300 plc ,and through a cp342-5(no-d-DP mode), communicate with an ET200 remote station ?

"No DP" mode is a selection you can make in the hardware configuration for any S7 controller. IF this selection is made, the CPU will not act as a DP master nor will it communicate via S7 protocol. This selection effectively turns off the DP port on the CPU for which "NO DP" is made. If the ET200 remote station is set up as the CPU Master, the answer to your second question is no, since the S7-300 would need to be set as "DP Slave", not "No DP". OF course a Industrial Ethernet connection could be made if it is available on both nodes.

Thanks a lot , now I understand , it seems the communication topic between plc's and/or ET's is a vast topic and it needs a lot of search and reading Siemens documents , for further understanding. for example when or not to use the DP_Send/DP_Recv or load/transfer , DPWRT/DPRT , i_GET/I_PUT ........ and this is depending on what type of plc's and ET's and operating modes and via cps or not .....
I hope one day you make tutorials on this topic and highlighting the use of this commands, in projects.
And finally i want to say : Realpars is the Perfect place to learn PLC .
Thanks again Realpars .