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REGARDING MULTI SLAVES IN CP341

Created by: samkcr at: 5/17/2009 6:52 PM (4 Replies)

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5/17/2009 6:52 PM	Rate (0)
samkcr Bronze Member Joined: 3/24/2009 Last visit: 8/7/2023 Posts: 406 Rating: (3)	HI all.... How tomodify the program for CP341 modbus masterfor connecting2 slaves(energy meters)? The example program was suitable to only one slave. I also tried for obtaining the communication of those 2 slaves and i obtained the values. But the problem was i am facing delay while obtaining the values and i tried to reduce the delay but the values are overlapping in b/w the corresponding DBs. I also attach the program what i used plz check the program. In the attached program i used the FC20 for meter looping. I am moving the corresponding DB.N0 to MW160 addr which is used in FC23 Those who are all know the solution kindly help me to solve this.... Thanks in advance.... Attachment zXX21_04.zip (250 Downloads)
	All is well :-)
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5/20/2009 8:22 AM	Rate (0)
venkat_2210 Posts: 12 Rating: (0)	Hi Sam, It would be works, Regards, Sora
venkat_2210 Posts: 12 Rating: (0)
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6/9/2009 5:28 PM	Rate (0)
samkcr Bronze Member Joined: 3/24/2009 Last visit: 8/7/2023 Posts: 406 Rating: (3)	Hi... No one has the solution for this? Still i didn't get reply....
	All is well :-)
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6/9/2009 6:26 PM	Rate (1)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/19/2025 Posts: 12344 Rating: (2707)	Hello samkcr; You could try this: Prepare two sets of functions Send/Recieve with the appropriatley prepared DBs for each slave. Trigger them individually to test the comms with each slave individually. Notice the output of the Recied FC named NDR: "New Data Recieved" It becomes active when the expected data is recieved without error. *How Data Reception is Displayed* The user is informed of data reception in the CPU by means of an edge at output *NDR. At this point the length of the received data block is displayed in the parameter* *LEN*. (Extracted from the manual Loadable Driver....Modbus RTUMaster). You can wait for the acknowledge of reception by the NDR output to trigger the Send FC for the second slave, and wait for the NDR from the 2nd slave's Recieve FC to trigger the first slave's send.... Noticew you will also need a startup trigger to start the cyclic call of slaves. You will also have tomonitor the status of the Send and Recieve FCs so you don''t get stuck in the program because the NDR does not come up. Another way I have used when repies are steady is to use a timer/counter combination to generate separate cycliucally triggers to each Send FC. But that is more touchy: itrequires extensive testing of all slave's comms, and undersdtanding of each s;ave's comm. delays so you are sure you will not trigger one while the other is operating. In any cse, please study the example programs provided in the Modbus master manual, they really are the basis of any development for a Siemens Modbus RTUmaster Hope this helps, Daniel Chartier

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6/9/2009 8:29 PM	Rate (0)
samkcr Bronze Member Joined: 3/24/2009 Last visit: 8/7/2023 Posts: 406 Rating: (3)	Hi... Thanks a lot for your reply... From this i understand that before making the trigger of the next slave we have to consider the status of the NDR right.... In the example says DB41.DBX0.4 is the NDR status may i use this ? And also i have one question. If i have to use seperate DB and FCs for each slave send & recieve fn the memory will increase ( in the case of connecting more slaves also) In my case i only use the different DBs for each slave for recieving the values so the memory is less.....But the problem is overlapping.... Do you have any idea about this overlapping why it is happenning (bcoz of NDR) ? Awaiting for your reply.....
	All is well :-)
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