comutation Master Slave MODBUS in S7 200

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Hi
I want to use S7 200 in MODBUS on Slave Mode .When it detects that his Master is absent , It must commutate in Master Mode to replace his XMaster in The networks.
so i used the MODBUS library and Microwin sp5.
my problem consiste of:
if the S7 200 comutate from Slave to Master Mode the comunication is blocked.
the cross-reference has show that the maker of the subroutine MBUS_CTRL has used the SM0.1.
so we can used this subroutine in my application one time and i can't access to this because hi is protected with password.
can any one have a solution for this probleme or he have the key for this subroutine.
thx

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The Modbus protocol is simple and well documented. Depending upon your requirements you may not need to impliment every function code. In which case you write your own routine. I did one some years ago to overcome another problem and it was fairly easy to do.

Thing to remember is what happens when the original comes back online. Your slave turned master will be sat quite happily controlling the bus when the original master will try and establish communications, you are going to end up with an undefined situation. Assuming original master is brought on line manually then you would have to build in a facility to switch your s7-200 master back to a slave at the same time. It can be done, but would need some thought.

the S7 200 in slave mode has not automatiquely turned to master

the comunication has blocked and i d'nt receave any thing.but if it connect in master mode first the routine has wrocked normaly .
i think that the subroutine MBUS_CTRL are a probleme if he has not execute first in start of plc.