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Redundant Modbus in S7-400H

Created by: ShahinM at: 10/19/2006 10:39 AM (5 Replies)

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10/19/2006 10:39 AM	Rate (0)
ShahinM Silver Member Joined: 11/8/2005 Last visit: 6/5/2024 Posts: 335 Rating: (3)	Can I use two CP441 in S7-400H for redundant Modbus network without writing any additional logic?In this condition can I put the same Modbus address for both CP441 or not?

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10/21/2006 4:41 PM	Rate (1)
Late Platinum Expert Joined: 1/7/2006 Last visit: 11/17/2023 Posts: 2705 Rating: (318)	[quote user="SM"]Can I use two CP441 in S7-400H for redundant Modbus network without writing any additional logic?In this condition can I put the same Modbus address for both CP441 or not? Hi, Thats not possible, the mayor problem is that the Modbus Master is most of the time one system, or they have two Modbus Master that only switched when the other is switched down. Normally it is possible to make two different point-to-point Modbus Master-Slave communications whereby the Modbus Master is deciding which Slave will be called, when there is nothing asked to the other slave then the slave gives no answers. When there is going something wrong with the Master then the other Master is going to ask his slave. It is also possible to get a Multidrop line with RS485 where both Masters (or only one) isreading/writing to both slaves the Registers and Coils, whereby the Slaves have different Slave addresses, the Master have to detect which communication is not working any more and have toread/write to the other slave. Or both slaves getting all data and in the S7-41xH this is controled...
	I hope that the answer will help, if you have still questions, don't hesitate to ask me. All the best, Late Never say never, think in solutions, not in trouble......
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1/21/2007 6:17 PM	Rate (0)
Techy Posts: 86 Rating: (2)	I am facing the same situation and this infohelps. One quick question - How do I detect the which CPU is the master ( any specific SFC to be called) Thanks
Techy Posts: 86 Rating: (2)
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4/27/2007 8:04 AM	Rate (0)
Robert vAd Member Joined: 4/27/2007 Last visit: 4/27/2007 Posts: 1 Rating: (0)	Hello, I'm facing the same problem Is there a work around for this problem? If it is possible are there special requirements for this modbus connection? Attachment Redundant Modbus.JPG (690 Downloads)

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4/27/2007 10:43 AM	Rate (1)
Aret Posts: 2348 Rating: (264)	You can use SFC. Here is code (SCL): i : INT; tbool: BOOL; SSL_Head : STRUCT lenthdr: WORD; n_dr: WORD; END_STRUCT; SSL_Dest : ARRAY [0..15] OF BYTE; i:= "RDSYSST" (Req := 1, SZL_ID := w#16#71, index := w#16#0, busy := tbool, SZL_Header := SSL_Head, DR := SSL_Dest); "LibStates".Master_in_Rack0 := (SSL_Dest[2] AND b#16#10) <>0; "LibStates".Master_in_Rack1 := (SSL_Dest[2] AND b#16#20) <>0;
Aret Posts: 2348 Rating: (264)
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4/28/2007 2:02 PM	Rate (0)
Late Platinum Expert Joined: 1/7/2006 Last visit: 11/17/2023 Posts: 2705 Rating: (318)	Hi Techy, See the FAQ when you have no SCL: reading out the operating state and status of an H systemthere is a FB253 which you may use and where the data of the master is directly shown to you.
	I hope that the answer will help, if you have still questions, don't hesitate to ask me. All the best, Late Never say never, think in solutions, not in trouble......
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