S7-300 Master slave profibus dp communication

[kader2007]

HI Everyone, I have an application where i have 2 CPU315-2DP talking to each other directly using the profibus DP (Master ==Slave). i would appreciate it if you could send me an example on how to use SFC72 and SFC73 to enable them to talk to each other, any other suggestions are welcome (I did manage to use SFC14, 15 but i don't want that method). Many thanks for your help. Kader

[Groo]

Have you thought of using a DP coupler, no special code needed then, acts like normal IO, very simple.

[kader2007]

Hi, Thanks for the reply. Unfortunatly i have havn't got a coupler. this is a test that i am doing because i am going to undertake a project where s7-300 set as a master communicating with other slaves ( s7-300's, festo valves..etc). the hardware i have is: CPU 315-2DP set as a master and CPU314C-2DP set as a slave directly connected via profibus dp. I got the communication working using SFC14, SFC15 but i think it is limited to 32 bytes ?! not sure but i am going to do more tests to see if i can transfer more than that..Also, because i have used siemens for 6 years i thought to post my question maybe i am imssing a very simple solution.. As you mentionned that's a perfect solution if i am using a coupler which you never know i might use in the near future. Thanks Kader

[kader2007]

Hi, Using the SFC14 and SFC15 does work fine but unfortunatly you are limited to 16 words (ie: 32 bytes), i will have to look for another sfc, may be SFC65, 66, 67 or 68, i will have to give it a go and see if i can transfer more than 32 bytes. Thanks for your help. Kader

[s7xp.com]

Correct SFC14 and SFC15 are 32 bytes maximum. Just configure more than one 32 byte I/O and use more SFC14 and SFC15's. The maximum per slave is 240 bytes. If you have more data, use a multiplexer method. Pratically the only problem is the number of I/O of the processor. Otherwise use a CP342-5.