Profibus slaves and OBs

Hello to everyone!

I am trying to understand communication between the PLC and its slaves but it's getting hard. So I hope you can help me.

HW: Master: CPU 400 - DP
Slaves: ET200S (DPV1)

When one of the slaves is switched off (power off) I understand that OB82 is executed. Is this rigth?

When that slave is switched on (power on), is also OB82 executed? And what else? What kind of conversation is between PLC and IM? Can I force the same kind of conversation by S7 programm for example when an input is active?

If this is posible, I will aprecciate an example of the programm.

Thanks.

OB82 is executed when a module with diagnostic capability detects an error.

If one of your slaves loses power then one of the side effects is that the bus communication, MPI or Profibus-DP, fails. In this case, OB84 is executed. OB84 is also executed when the power returns and the bus communication is once again available. To keep track of the state of your Profibus slaves you can use FB125 (detailed diagnosis) or its little brother FC125 which will simply tell you which slaves are in fault, but not give any details.

You can download both these from the Siemens support website. You can run FB125 / FC125 either inside OB84, on demand so to speak, or else cyclically from OB1.

OB84 will also report Memory errors in the CPU, errors in the CPU OS and performance problems in a 400-H system. All of these errors are extremely rare in comparison to bus problems, though.

Hello,

you can evaluate the difference between power off and power on with the OB82_EV_CLASS in OB82 : #39 means incoming event (power off) and #38 means outgoing event (back to normal, power on). You can use this in combination with the time of the PLC clock, so you always know when a error occured, also can write the other events to another block if you want to know what happened. Greetz

Thank you RMA. I understand better now.

But one doubt yet. When the power returns, the CPU notice it and then OB84 is executed. So, how the CPU notice that? Can I do the same effect without switching off the slave?

I am asking this because I think sometimes my CPU doesn´t notice that the slave is active again. Maybe, because there are a lot of slaves switching on at the same time, so the profibus communication is to full........If I swicth only one by time everything works ok.

Any advice about this? where can I read about this?