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What is the minimum stub lenght for Modbus RTU ( RS-485) ?

5/6/2016 7:37 AM	Rate (0)
Prime26 Posts: 2 Rating: (0)	I woiuld like to know what is the minimum length of cable to use if I have to connect a communication cable from a PLC 1200 to a drive ( Yaskawa V1000).
Prime26 Posts: 2 Rating: (0)
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5/6/2016 10:55 AM	Rate (1)
Duris_I Diamond Expert Joined: 4/28/2015 Last visit: 3/26/2025 Posts: 10837 Rating: (836)	Hello, with 2w RS-485 I had also 10 cm long cable with dsub connectors without problems, but with other type device. Do you have some doubts, special requirements, infos?
	Last edited by: Duris_I at: 5/6/2016 10:56:06 AM With best regards... Ivan Duris Flight: OMICO
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This contribution was helpful to 1 thankful Users Prime26

5/6/2016 11:31 AM	Rate (1)
Navnag Platinum Expert Joined: 11/21/2007 Last visit: 3/16/2025 Posts: 2326 Rating: (309)	Hello This would be more a condition imposed by RS485 hardware rather than the protocol. Some guidelines suggest that minimum cable length should be 0.3m ( See attachment Page-4). Short lengths can cause communication issues at higher baud rates ( e.g. for Profibus RS485 networks with speeds in MBPS ). For normal baud rate of 9.6kBPS generally used in Modbus RTU Normally it may not be so significant. Still there is no harm in following this rule. Hope this helps Cheers Navnag Attachment wiring guidelines for rs-485 networks.pdf (501 Downloads)
	There is no such thing as the last bug in a program There are no stubborn bugs, There are only stubborn Debuggers.
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This contribution was helpful to 2 thankful Users Duris_I Prime26

5/6/2016 12:49 PM	Rate (0)
Prime26 Posts: 2 Rating: (0)	Hi guys thanks for the reply and information. it was extremely helful especilly the pdf attached. from the information you gave, we going to use 0.3 m to avoid communication issues. thank you @Doris_I In this case I am not using connectors, I am using wire to terminal so I had doubts especially when comes to the lenght. Regards... @Navnag The pdf was very helful and I am probably going to use 9.6 KBPS for this particular project. cheers.
Prime26 Posts: 2 Rating: (0)
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This contribution was helpful to 2 thankful Users Navnag Duris_I

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