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Why we are not using modbus

Created by: Amolthorat at: 6/20/2007 10:29 AM (2 Replies)

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6/20/2007 10:29 AM	Rate (0)
Amolthorat Posts: 3 Rating: (0)	dear all I want to know that why we are not using modbus insead of profibus. and what are diffrences between these two protocols.
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6/22/2007 12:07 AM	Rate (2)
Late Platinum Member Joined: 1/7/2006 Last visit: 5/11/2025 Posts: 2705 Rating: (321)	Amolthorat I want to know that why we are not using modbus insead of profibus. and what are diffrences between these two protocols. Hi, Modbus versus Profibus: Modbus is an old (one of the first) protocol from Modico Gould, it have a lot off overhead and is mostly used by American firms. There are some different uses, Modbus RTU, Modbus ASCII and Modbus TCP. The first two are very slow, this is because there is a very big checksum on it and you can have only one master. The highest baudrate I have seen is 56k6 bit/s. With the Modbus TCP is some faster datacommunication possible, but it is also not that fast like for example Profinet which is also a Ethernet-based protocol. Siemens have all 3 the Modbus protocols. The first two on a CP 341 or a CP 441-2and the thirth one ona CP343-1 or a CP443-1. Profibus is a already based protocol which is grown from SINEC L2 from the late 80'sto Profibus DP/FDL/FMS in the early 90'sand now also to Profinet. For Profibus DP it is possible to use on 12Mbit/s and it is then deterministic. There are also possibilitys for synchron busses and the target rotation time is determined by the slaves you are using. It is possible to have more masters on one network. There are about 1200 companys who make equipment for Profibus DP and already 16.000.000 nodes placed. Profibus FMS is an objectbased protocol, it is rarely used. Profibus FDL is communication with the "old" world such as SIMATIC S5. I prefer Profibus and now more and more Profinet to use, but sometimes the equipment is that old that it only can use Modbus, so that it have to be maked with Modbus. With Profinet RT it is possible to communicate with bustimes of 4...10ms. When using Profinet IRT it is possible to communicate with 250 microsecond with a jitter of 1 microsecond. This is specially for drives that have to be synchron, but could also be used for I/O.
	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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7/12/2007 3:09 PM	Rate (0)
Amolthorat Posts: 3 Rating: (0)	Dear Sir, thanks a loy for your valuable reply.
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Why we are not using modbus

Created by: Amolthorat at: 6/20/2007 10:29 AM (2 Replies)

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