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Slow Modbus communication

Created by: Ducolares at: 6/13/2007 6:24 PM (6 Replies)

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6/13/2007 6:24 PM	Rate (0)
Ducolares Posts: 12 Rating: (0)	Hello all, I have a system with two reduntant PLC S7400 series (417-4H) connected to S300 I/O cards, using Profibus DP (IM153-2). The software was built using PCS7 6.1. We have aModbus communication with a third party system using a CP 341-RS422/485 modbus interface card. The problem is that the communication between our CPU and this third party system is getting very slow response times, about15 sec for refreshing data. We are using a S7HMODM3 Function Block to receive their data. Any suggestions to get this communication faster, or at least find out what is making its so slow? Best regards, Eduardo Colares
Ducolares Posts: 12 Rating: (0)
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6/14/2007 7:10 PM	Rate (0)
Late Platinum Expert Joined: 1/7/2006 Last visit: 12/23/2024 Posts: 2705 Rating: (320)	Dear Eduardo, In which time-OB is this block, when the call is not that fast then you have already some delay, the telegrams are divided into blocks that are going on IO-base to the CP 341. You can find in the handbook of the CP 341 some where on the end how many time is used to transfer a certain amount of data. So when you could do something about the length of the data then you win also time. But 15 seconds is very much, when you couldn't find anything then there must be something else wrong.
	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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6/5/2009 7:13 PM	Rate (0)
pavan_dath Posts: 2 Rating: (0)	KIndlylet us know whether this problem isovercome and also what is tehway we can chechk the differentproblems(Probable)
pavan_dath Posts: 2 Rating: (0)
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6/5/2009 7:52 PM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 12/10/2024 Posts: 2957 Rating: (243)	I just want to ask how much slaves you have and what is connection speed ?
	Best regards, Darius
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6/6/2009 6:19 AM	Rate (0)
pavan_dath Posts: 2 Rating: (0)	We have connected 3 Slaves and teh speed set is 9600 bps Individually the meter communicates without any problem and when we attempt to put the three into Network this problem occurs At a time we are polling 6 registers
pavan_dath Posts: 2 Rating: (0)
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6/6/2009 8:44 AM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 12/10/2024 Posts: 2957 Rating: (243)	Yes, it should be a little bit faster I think. 2-3 seconds maximum.
	Best regards, Darius
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6/13/2009 9:39 AM	Rate (0)
Paresh Posts: 116 Rating: (1)	can you increase communication speed beyond 9600bps?
Paresh Posts: 116 Rating: (1)
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