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Modbus General Description

Created by: smiffy at: 12/15/2011 6:41 PM (57 Replies)

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5/6/2012 1:08 PM	Rate (0)
gre_m Posts: 947 Rating: (45)	modbus exist on rs422/485/232 as add on over ptp-communication and add-on over ethernet/TCP=modbus TCP. Profibus - is all-sufficient prtocol, therefore modbus as add-on over profibus not exist.
gre_m Posts: 947 Rating: (45)
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5/6/2012 2:05 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 8/21/2024 Posts: 1545 Rating: (537)	I think they were hinting that I could do a similar document to explain the basics of Ethernet and Profibus (and maybe even Profinet). I don't think that they were suggesting that modbus can be setup over a Profibus interface. I will see what I can do to come up with Ethernet and Profibus documents. However, these things tend to take quite a bit of effort and time. I will also need some proof reading services from my fellow experts.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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This contribution was helpful to 2 thankful Users REZA_SHABANI Prosto

5/6/2012 4:02 PM	Rate (1)
Arunraje Posts: 94 Rating: (8)	Ya Smiffy please do the needful... Regards.
Arunraje Posts: 94 Rating: (8)
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5/6/2012 8:08 PM	Rate (0)
AUTOMATION_BOUHA Posts: 2 Rating: (2)	Thank u SMIFFY thats nice from u, that will help us more, and i hope that we don't bother u
AUTOMATION_BOUHA Posts: 2 Rating: (2)
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5/7/2012 1:11 PM	Rate (0)
Aniket S Dange Posts: 22 Rating: (3)	Dear Arun, this will surely help you.. http://www.plcmanual.com/isoosi-model Enjoy..
Aniket S Dange Posts: 22 Rating: (3)
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This contribution was helpful to 1 thankful Users Arunraje

7/20/2012 4:00 AM	Rate (0)
YvonV Posts: 29 Rating: (0)	its a good read. thank you for that effort. Yvon
YvonV Posts: 29 Rating: (0)
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This contribution was helpful to 2 thankful Users smiffy sorooshi

9/29/2012 9:21 AM	Rate (0)
Hunky Posts: 82 Rating: (5)	Thank you for the support. I am a little confused here. I am doing a project where in i have to communicate with ABB DCS with CP 441-2. The following is the requirement. Data from DCS to PLC Analog Output - Address : 400001 Digital Output - Address : 00001 Data from PLC to DCS Analog Input - Address: 300001 Digital Input - Address :100002 In the above circumtances,CP 441-2 shoule be acting as Slave / Master? If it is acting as a Slave will it read the data from DCS. Thanks for your support and co-operation. BR MIA
Hunky Posts: 82 Rating: (5)
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9/29/2012 12:37 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	Hello Hunky, the used addresses do not imply any information which communication partner is master and which one is slave. It depends ontheapplication on site. The master is the active one, it can read data fromand write data to the slave. The slave can't initiate communication, it can just answer the client's requests. You have just to ask whether the DCS acts as master or not. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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This contribution was helpful to 3 thankful Users dchartier mihihmjakds Ethree

9/29/2012 12:42 PM	Rate (1)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 9/8/2024 Posts: 12282 Rating: (2682)	Hunky Data from DCS to PLC Analog Output - Address : 400001 Digital Output - Address : 00001 Data from PLC to DCS Analog Input - Address: 300001 Digital Input - Address :100002 In the above circumtances,CP 441-2 shoule be acting as Slave / Master? Hello hunky; It is indifferent which of the 2 (CP 441-2 or DCS) is master on the bus, especially if you have only these 2 nodes on Modbus RTU. Choose one to be master based on ease of programming and familiarity, If you select the DCS as master, you will have to program the Modbus jobs in the DCS, and choose: - Write multiple coils (Modbus function 15- write to the 0000x outputs of the PLC) -Write multiple registers (Modbus function16- write multiple 4000x registers to the PLC) -Read input registers (Modbus function 04- request 3000x registers from the PLC) -Read discrete insputs (Modbus function 02- request 1000xinputs from the PLC) Of course if the roles are reversed you would have to select the Modbus jobs in the Cp 441-2 so you would write digital and analog inputs to the DCS, and read digital and analog outputs to the PLC. The slave will only reply to the master when Modbus jobs are sent to it, so everything is to be planned from the master's point of view. I do not know how difficult it is to use Modbus RTU on your DCS, but it might be easier to let the CP 441-2 act as a slave, therewould very little programming to be done on that side. Have a look at the following sample program for Modbus slave functions proposed by member Amit recently: /tf/WW/en/Posts/72742 Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 9/30/2012 5:22 PM
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10/3/2012 12:16 PM	Rate (0)
Saggy Silver Member Joined: 11/8/2011 Last visit: 8/21/2024 Posts: 387 Rating: (43)	Thank you its very useful,I hope that you can explain to us more about profibus and ethernet protocols

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