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CP341 Modbus Slave RTU

Created by: Nil96 at: 7/21/2008 2:29 PM (4 Replies)

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7/21/2008 2:29 PM	Rate (0)
Nil96 Posts: 325 Rating: (14)	Hi, We are executing a project which has 313CPU & CP341 Communication Card. The idea of CP341 is to share data with existing DCS of the client & this happens thru Modbus. In our earlier projects we have used CP341 as master & the blocks used were FB7 & FB8. Every thing is working fine. My doubt is::-> in the current project shud we still use FB7 & FB8?? When the parameter settings for CP341 are opened, if thememory ranges & DB start address are configured, will the modbus slave rtu communication be successful?? Need some advice plz. Cheers Nil
Nil96 Posts: 325 Rating: (14)
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7/21/2008 4:23 PM	Rate (1)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 12/27/2024 Posts: 12316 Rating: (2696)	Hello Nil96; The communication FB (Modbus RTU sk lave) for CP341 is FB80, and for CP441-2 it is FB180. They are much easier to setup than the Modbus master functions. What you need to understand is how the Modbus addresses are interpreted by the CP341 slave, and how they are mapped to different memory areas of the S7 PLC. The following manual is very explicit on how the different base addresses + offest can be calculated for different Modbus functions (see chapters 1 and especially8): http://support.automation.siemens.com/WW/view/en/1218007 When you install the Modbus slave functions in your Step 7 software, different Modbus examples are loaded into your libraries so you can follow them to illustrate the manual's explanations. Hope this helps, Daniel Chartier

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7/22/2008 6:09 PM	Rate (0)
Nil96 Posts: 325 Rating: (14)	Dear Daniel, Thanx a lot for ur reply. I tried FB80. The only blocks I inserted was FB80,DB80 & OB1. H/w consists of CPU312 & CP341. Downloaded the entire pgm, but the CPU is going into system fault. Online Diagnostic Buffer says that " Area length error" & this points to FB80. CHeers Nil
Nil96 Posts: 325 Rating: (14)
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7/23/2008 9:54 AM	Rate (0)
Nil96 Posts: 325 Rating: (14)	Hi Daniel, Was able to communicate. The problem was very general. Earlier when I downloaded the pgm, used to get "area length error" and it was pointing to FB80. This error went away when I first inserted FB7 & FB8, and then I trid to insert FB80 in OB1. Thanx a lot for ur advice and the link for the manual which u gave. Cheers Nil
Nil96 Posts: 325 Rating: (14)
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11/30/2009 8:35 PM	Rate (0)
tesco Posts: 1 Rating: (0)	Hi, This happened to me before and I was able to make it work by delete DB80 and recreate it.
tesco Posts: 1 Rating: (0)
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