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Modbus with a Siemens system

Created by: Bryll at: 5/21/2013 9:00 AM (16 Replies)

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5/21/2013 9:00 AM	Rate (0)
Bryll Posts: 168 Rating: (5)	Amit_86 Dear All, Hereby i am attaching Modbus Slave Program for ready reference. In this reference project, CP341(RS485) is Modbus Slave and Yokogawa DCS is Modbus Master(RS232). you can find Sample Program with Mapping Details in Excel FIle and Cable Configuration as well. Hope this will help to understand Modbus Slave Concept eailsly ans especially to those who are Configuring Modbus Slave for the first time. Attachment:Modbus Slave Program.zip (544 Downloads) Hi Guys and Gals, I'm new to Modbus with a Siemens system, I've done several Modbus communications with other systems before. But, Siemens doesn't look the least similar to what I'm used to I've checked the example code provided here and find it quite useful, but I have a few questions. Can I use a DB selected by me for the data transfer, in HW config somewhere ?? Where do I specify what DB I'd like to use for the data exchange, HW config ?? Is it possible to use one DB for TX and another for RX ?? Do I need to specify the length of the transmission and reception ?? Cheers
Bryll Posts: 168 Rating: (5)	Last edited by: O_Moderator at: 5/27/2013 9:50 AM new subject after splitting from /tf/WW/en/Posts/72742#top
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5/21/2013 3:42 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello Bryll, the used data block depends on the register address in the request and the parameterisation of the driver in PtP-Param (base DB number). It is not possible use different DBs for read and write requests of the master when he addresses the identical register (e.g. holding register 100 is always the same data word in a DB). Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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5/21/2013 7:17 PM	Rate (0)
Bryll Posts: 168 Rating: (5)	Cheers Kaulquappe, thanks for the reply. So if I understod you correctly am I forced to use DB4 for data storage, if the master asks for Modbus address 40001 will the modbus block FB80 automatically send away DB4.DBW0. Was this correct ?
Bryll Posts: 168 Rating: (5)
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5/22/2013 10:58 AM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello Bryll, which DB number would you like to use? Just insert this number in the menue FC3/6/16 as base DB number when parameterizing the Modbus slave driver. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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5/31/2013 1:31 PM	Rate (0)
Bryll Posts: 168 Rating: (5)	I think I understand the procedure of how to set up the modbus communication on the 300 system in Step7 Classic a bit better now. 1. I have to download a driver setup software and install it before I can initialize the communication module. 2. Install the required FB's in the software of course, and organize all the data to be transferred between the PLC and the DCS. 3. Initialize the communication module. Do I put in my DB address here for the data to be exchanged with the DCS? I downloaded of course the wrong software to initialize the module Now when I'm trying to install the one that I think is correct can't I find it, it seems to me that the one already installed is reinstalled. Anyone else that got this experience or anyone having a solution for this?
Bryll Posts: 168 Rating: (5)
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5/31/2013 10:37 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/19/2025 Posts: 12344 Rating: (2707)	Hello Bryll; Sorry if this is unnecessary, but before step 1 in your list there is another importantstep: Purchase of the correct license for Modbus RTU, and insertion of the hardware dongle (included in the driver delivery package) in the slot at the back of the CP 341 you are using in the project. Which drivers can be loaded for the serial communication processors? What should you watch out for when programming the communication blocks for Modbus S7-300 CP341 as a slave? If this step has been taken care of already, please give us more information about the "wrong software to initialize the module" that you downloaded, and on the driver you believe you need now and cannot find. Maybe we can help. Loadable Driver Modbus Slave (RTU) Download CD "CP340, CP341, CP440, CP441" Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 5/31/2013 10:37 PM
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This contribution was helpful to 1 thankful Users Bryll

6/11/2013 7:11 AM	Rate (0)
Bryll Posts: 168 Rating: (5)	Hi Daniel, How stupid can a man be , of course do I need to buy a license to do this. I will never learn that when working with Siemens is it never enought to buy the HW, one has to buy a SW license too. Thanks Daniel for making this clear to me, don't know how I could have missed that. I'm just not used to have to buy SW licenses to get something working, normally it's just to buy HW and write some code and it works.
Bryll Posts: 168 Rating: (5)
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6/11/2013 12:52 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/19/2025 Posts: 12344 Rating: (2707)	Hello Bryll; And welcome to the world of Siemens PLCs... Daniel Chartier

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9/2/2013 9:52 AM	Rate (0)
Bryll Posts: 168 Rating: (5)	Hi again, I'm about to test the communication any day now, but I'd like to be sure I've got everything correct before I'm at the customer. Not sure if I got the correct driver installed. When I try to set the protocol parameters for the CP341 do I have the following choices: 3964(r) RK512 ASCII Printer Sounds to me that I got the wrong software installed ?? Where shall I set the slave address, in software or hardware config ? I think I understod the addressing of the DB I use for the data tranfer. The master is addressing the DB in the MSB of the data block when specifying the modbus function code (LSB). Getting a bit confused here
Bryll Posts: 168 Rating: (5)
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9/2/2013 12:32 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 3/10/2025 Posts: 1557 Rating: (540)	Have you loaded in the loadable Modbus drivers yet?
	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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