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| 7/6/2012 3:12 PM | |
Joined: 9/27/2006 Last visit: 3/20/2025 Posts: 12344 Rating:
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Hello Naveen; As a prelude I must say that I have not worked with this particular Bacnet to Modbus gateway before, but I have had opportunity to use others (from Trane, York...) and have faced similar problems. So let's see if I can point you in the right direction. I am not aware of the depth of knowledge you have with Modbus RTU, but just as a refresher I can suggest our friend smiffy's excellent presentation on basicModbus functionnality: Modbus General Description Of course, more specific details can be found in the Modbus master and slave manuals provided by Siemens, such as this one: SIMATIC S7-300/S7-400 Loadable Driver for Point-to-Point CPs: MODBUS protocol, RTU format, S7 is master Our main issues when mapping data from the Bacnet to the Modbus addresses generally come from selecting the wrng Modbus addresses. Digital inputs (boolean)should be mapped to 10000x Modbus addresses, and the Modbus master (the PLC) should be using Modbus Function 2 to read all your digital inputs at one time. What Modbus functions are programmed for your Modbus master (I presume it is a CP 341 or a ET 200S 1SI), how are they mapped to the DBs in your program? If you could give us an idea of the CP module data, the connection standard (RS-232, RS-485) and the program blocks you use it could be helpful. Hope this helps, Daniel Chartier |
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