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Et200s modbus serial moduleLine Terminator (End of line resistance)???

Created by: Ahmed Ganainy at: 7/18/2010 10:51 AM (13 Replies)

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7/18/2010 10:51 AM	Rate (0)
Ahmed Ganainy Experienced Member Joined: 8/22/2009 Last visit: 7/11/2024 Posts: 42 Rating: (1)	I am using our ET 200S Modbus serial interface module (6ES7138-4DF11-0AB0) I have 18 module (from the above reference) distributed in 14 Et200s nodes. All my slaves (MCCs from schneider) and all of them are motor starters. My question: These motor starters need line terminator 150 Ω. and our modbus module talk about 330 Ω in both sides. To complete the image. My control panels located in mcc rooms so maximum distance about 20m. I am using RS485 with about 15 nodes per modbus module. which one i have to choose 150 or 330 .....? Et200s serial module manaul haven't talk about modbus hardware for network(multi-node) and maximum tap off distance.
	Veolia Engineering Team
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7/21/2010 12:01 PM	Rate (0)
Ahmed Ganainy Experienced Member Joined: 8/22/2009 Last visit: 7/11/2024 Posts: 42 Rating: (1)	WAITING FOR YOUR HELP
	Veolia Engineering Team
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7/21/2010 4:37 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 9/10/2024 Posts: 12282 Rating: (2682)	Hello Ahmed; Could you please show us where you see the requirement for 330 Ohms as line termination for your 1SI module? Modbus serial standards require a 150 Ohm termination on mutipoint (RS-422 and RS-485) systems, and this is the requirement I have followed on every Modbus line I have setup. Here is a quote from the Modbus over serial lines document, from Modbus.org: MODBUS over serial line specification and implementation guide V1.0 Modbus.org http://www.modbus.org/ 28/44 12/02/02 Each line termination must be connected between the two conductors of the balanced line : D0 and D1. Line termination may be a 150 ohms value ( 0.5 W ) resistor http://www.modbus.org/docs/Modbus_over_serial_line_V1.pdf Hope this helps, Daniel Chartier

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7/24/2010 7:30 AM	Rate (0)
Ahmed Ganainy Experienced Member Joined: 8/22/2009 Last visit: 7/11/2024 Posts: 42 Rating: (1)	kindly explain this to me. Attached file is the page talk about 330 ohm line terminator. Attachment Terminating resistor.JPG (378 Downloads)
	Veolia Engineering Team
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7/25/2010 4:34 PM	Rate (1)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 9/10/2024 Posts: 12282 Rating: (2682)	Hello Ahmed; Sorry, I cannot explain this, as you say. Standard Modbus requires 150 Ohm termination, as my experience tells me and Modbus standards specify. But for all types of connection, RS-232, RS-422 and RS-485m the 1SI termination resistors are listed witha value of 330 Ohm, as shown in your attachment and in the 1SI Modbus manual... So it would seem that the best course would be to follow the manufacturer's recommendation, and go for the 330 Ohm value (although I would like to understand why this value was selected by Siemens, being non-standard for Modbus applications). In any case, I would choose a very low bus speed, 9600 Baud for example, so that the network would not be as sensitive to line mismatch issues. Modbus can be very forgiving at low speeds; you can even design long spurlines at that speed, even though the standard dislikes them. Hope this helps, Daniel Chartier

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9/27/2010 7:28 PM	Rate (0)
technog Posts: 15 Rating: (0)	Hi Ahmed/Daniel I face the same situation. Ihave 10 networks with 1SI master, each with upto 22 slaves(Schneider MCC andpower-meters). Baudrate is set to 19200 since some nodes do not support lowerbaudrate. Nowwhen I useany of120, 150 or 330ohm resistors as line termination thenthe whole network fails andmy function blocks indicate either CRC errors orshow allnodes asdisconnected. But if use noline terminationthen alll nodes communicateperfectly wellalbeitwithone or two nodes droppingout for a few seconds after every10-15 minutes. Didanyone find any solution for the line termination? Secondly,is'nt the line termination supposed to matchwith the impedance of the cable, rather than being dependent on driving electronics?
technog Posts: 15 Rating: (0)
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1/25/2016 9:36 AM	Rate (0)
TgAutomation Posts: 63 Rating: (1)	technog " Nowwhen I useany of120, 150 or 330ohm resistors as line termination thenthe whole network fails andmy function blocks indicate either CRC errors orshow allnodes asdisconnected. But if use noline terminationthen alll nodes communicateperfectly wellalbeitwithone or two nodes droppingout for a few seconds after every10-15 minutes. " Hello Technog, and you all. I am having the same problem, started out with 120 then tried 330omh. I was wondering if you found a solution? I contacted the technical support and they told me to use 330ohm resistors, then I contacted them again and then they told me that 330ohm is only necessary on their side. And if the other side is a third party then I should use an end resistor according to their manual. This sound very strange to me because I thought that the physical layer of a bus does not have sides, it has ends that need termination. If I put 120ohm in each end then there is 60ohm between the lines, no matter if you measure in one or the other end. My problem is also that I don’t have the Siemens PLC (Master) on the end, it is someway in the middle and it has multiple third party slave devises on each side of it. I hope you can help me or maybe someone else. Regards, HannAri
TgAutomation Posts: 63 Rating: (1)
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1/25/2016 11:19 AM	Rate (0)
Duris_I Diamond Member Joined: 4/28/2015 Last visit: 2/7/2024 Posts: 10533 Rating: (820)	Hello Hann, can you provide pls schema of your network, maybe with distances between stations, speed?
	With best regards... Ivan Duris Flight: OMICO
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1/25/2016 12:07 PM	Rate (0)
Duris_I Diamond Member Joined: 4/28/2015 Last visit: 2/7/2024 Posts: 10533 Rating: (820)	Hello Hann, after your post I think about this situation, or isn't it? Look at atachment. I think that 330 Ohm resistor isnt strictly required, it all depends to cable characteristic and speed of transmission. Attachment Star network.jpg (317 Downloads)
	With best regards... Ivan Duris Flight: OMICO
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6/28/2016 12:54 PM	Rate (0)
TgAutomation Posts: 63 Rating: (1)	Duris_I Hello Hann, can you provide pls schema of your network, maybe with distances between stations, speed? Hi Duris. Its been a long time but i am finally starting on this project again. I drew up a simple schematic of the Modbus. The speed is 19200. Attachment IMG_0610.JPG (219 Downloads)
TgAutomation Posts: 63 Rating: (1)
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