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| 1/25/2013 4:34 PM | |
Joined: 9/27/2006 Last visit: 1/21/2026 Posts: 12481 Rating:
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Hello NEDCO; Let's see what ansewers can be provided to you various questions:
On a Modbus RTU network only one master is allowed, as per Modbus standards. So yes one of the PLCs will need to be configured as a Modbus slave. You can choose which one during your design phase.
Hex 0113 corresponds to dec 275, which reperesents the offset from the start of of the holding registers (function 3). So your address should be (start address, holding registers) 40001 + (offset) 275 =40276. The S7-200 Modbus instructions are weel described in the S7-200 System manual, you create your telegram (including the slave Modbus address, the start address of the first register required and the number of registers required) in the Modb-Msg instruction, after initializing Modbus comms and the Modbus master with functions Modb_Init and Modb_Ctrl. there is an example in ladder ro read and write some holding registers from a slave on pages 360-361. S7-200 System Manual Remember you will need to purchase the Microwin Modbus/USS libraries to use the Modbus functions described: http://support.automation.siemens.com/WW/view/en/10377278
I need to s7 200 modbus ex program You could have looked for this type of information yourself, using the search box at the right of this page. Try it, there are more threadsin the forum on this subject.
I do not believe you are aking the right question. You can connect up to 31 slaves to a master within one segment, and what is important is the distances covered. With good RS-4585 cable and correct connectors, termination and installation you can cover about a 1000 m in all, daisy-chaining your slaves. Hope this helps, Daniel Chartier |
| 1/25/2013 7:55 PM | |
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Joined: 9/27/2006 Last visit: 1/21/2026 Posts: 12481 Rating:
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Hello NEDCO; First, if you are going to use gprs, you might as well seperate the Modbus data collection between the Modbus master and the Sepam relays, and the s7-200 to S7-200 gprs communications. Have a look at these documents: Micro Automation: Wireless Data Communication based on GPRS (MAS 21) How can you ensure that all data sent from an S7-200 via GPRS is received? |
Last edited by: dchartier at: 1/25/2013 7:56 PM |
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| 1/26/2013 9:38 PM | |||||||||||
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Joined: 9/27/2006 Last visit: 1/21/2026 Posts: 12481 Rating:
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Hello NEDCO; Here is a list of equipment you would need for this project, on the Siemens side, with links to the Product Support page for each:
The last 2 items in the list are the 2 available models of S7-226 available, power requirements and outputs are different, you will have to select between the 2. The ports on the CPUs are standard RS-485 connections, so you need a Sub-D 9-pin connector for each, and connections at pins 3 (TXD/RXD+), 8 (TXD/RXD-)and 5 (Shield), You will find in the following link an illustration of the connections ot the S7-200 ports. It shows a connection for a USS protocol, but it uses the same RS-485 cable settings. How do you install a communications connection between an S7-200 and a MICROMASTER 4 via Port 0 (RS485) with EMC and overvoltage protection? Generally it is not recommended to transfer power and signal on the same cable for serial communications. We have had to change our cable setup on different projects because of this. Either use 2 seperate cables (and the comm. cable must have a shield), or use a single 2-pair cable if you must, each pairindividually shielded. Follow the connection diagrams for the Sepam relays to make sure you design the network properly; Sepam - RS 485 network connection guide Notice page 11, where they match their wire designation (A/B) with the standard TX RX names: A--¨> TX/RX- B--> TX/RX+ Hope this helps, Daniel Chartier |
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