Lost communication between PLC and Slave

Hello;

I have PLC(S7-400) and its slaves(Distributed Peripheries) and I want to have an alarm shown in CEMAT every time that there is no comunnication between PLC and this slaves. For instance every time the power source for the DP is lost. How can I activate a bit which indicates me that communication is lost, so I can send it to the CEMAT?

Thank you very much!!!

This may not be the exact solution which you are looking for but definatly it will give you an idea.
Ultimatly when you lose communication you are going to lose I/O
You can write some simple logic in OB 82 I/O Point Fault 1.
Basicaly by using diagnostic address of Profibus DP Slave (Which you can find that in Hardware Configuration of DP Slave) you can write follwoing logic in OB 82 genrate the Faults bits from DP Slaves.
Example : for more details see the attachment.
A(
L #OB82_MDL_ADDR
L 2035
==I
)
= #fault_1
A #fault_1
A(
L #OB82_EV_CLASS
L B#16#39
==I
)
S M 91.0
A(
L #OB82_EV_CLASS
L B#16#38
==I
)
R M 91.0
NOP 0

You Can also use OB87 Communication Fault.