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S7-400H - CP441-2 - Redundant slave Modbus

Created by: Seroj at: 7/28/2010 5:18 PM (4 Replies)

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7/28/2010 5:18 PM	Rate (0)
Seroj Posts: 4 Rating: (0)	Dear all .I am using S7-400H system with tow CP441-2 installed on each rack for Redundancy . Please advice me how to use THE CP441-2 modules as REDUNDANT SLAVE MODBUS-RTU . Which (FC , FB, SFC , SFB, OBs ) Required for this application . By the way I have installed the Slave MODBUS- RTU Driver with dongle in each module .
Seroj Posts: 4 Rating: (0)
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7/29/2010 3:07 PM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Dear Seroj, I am not sure if the MODBUS RTU function is released for the S7-400 H system at all. The only MODBUS solution released for the S7-400HI know of is the solution for MODUBUS TCP. But maybe someone else has a better knowledge about it than me. Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)
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7/29/2010 3:38 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 3/18/2025 Posts: 12344 Rating: (2707)	Hello Seroj; J_Bell is right in that only Profibus and Etehernet CPs are supported for redundant connections on S7-400H systems. Refer to the S7-400H manual for more details. Manual S7-400H Fault-Tolerant systems: http://support.automation.siemens.com/WW/view/en/1186523 Basically, the solution proposed is a CP 341, setup as a Modbus RTU slave in a redundant ET 200M chassis, with a single connection to the Modbus master's bus. This way, whatever the active S7-400 CPU, the connection to modbus is maintained at all times. You would simply program the CP 341 slave as a standard Modbus RTU slave, based on the Modbus slave manual. http://support.automation.siemens.com/WW/view/en/1218007 See the foolowing links: How do you download a loadable driver such as "Modbus Master (RTU)" into a CP341 that is connected to an S7-400 H system by means of an ET 200M? http://support.automation.siemens.com/WW/view/en/17854293 Does S7 400H support redundant CP441? (Note specially Late's post) /tf/WW/en/Posts/8389 If you choose to maintain your original configuration (CP 441-2) we have to think about the problems this could cause on the bus. Modbus allows only one master oin the bus at a time, but can live with a missing or defectiveslave, although this would probably slow down the bus cycle (through retries) and cause constant diagnostics in the master. Now, the basic problem is that only one of the CPUs is active at a time in the S7-400H system, and that CPs without redundant connections (such as a CP 441-2) will not be active on their bus when the CPU is inactive. Therefore they will not reply to the master's requests, and will be marked as defective in the master's diagnostics after a number of retries (programmable in the master's configuration). If you simplyattribute a distinct Modbus address to each slave CP 441-2, and program the master to repeat/duplicate its requests to every one, then at least one will respond correctly to the Modbus requests; the others would be marked as unresponsive. Program the master to use minimum retries on defective/missing slaves, and use the diagnostic data available to disregard data polled from the unresponsive slaves (it has a tendancy to take a value of 0), and your system should work. But you will have to test it properly to make sure you have taken care of the recurring diagnostics. Hope this helps, Daniel Chartier

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This contribution was helpful to 1 thankful Users J_Bell

7/30/2010 1:10 AM	Rate (0)
Seroj Posts: 4 Rating: (0)	Thanks to all -Serial Modbus Redundancy based on ET 200M chassis , I think it has limitation on number of I/O Bytes. I required at list 1230 Bytes . -Yes the other vender (master modbus) must take care of the Switching between the active modules . I think if I provide them the status of each CP 441-2 on both CPs , based on that they will be able to Marke each CP441-2 asunresponsive or stand by as follow :- 1- No response & normal status (from active CP) = stand by . 2- No response & faulty status (from active CP) = unresponsive due to faulty CP -But whatabout H-SYSTEM (slave Modbus) . How do I switch between The CPs as redundant salve-Modbus ? which (SFC –SFB – FC – FB) like FB180 must be used to recognize which CP are online and active with the master-Modbus ? For example : from which CP should I accept the start commandfor startingthe motor ? Regards
Seroj Posts: 4 Rating: (0)
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1/27/2015 2:07 PM	Rate (0)
Min_Moderator Platinum Member Joined: 9/3/2014 Last visit: 3/13/2019 Posts: 4766 Rating: (122)	New question published bymiguelbustosm... is split to a separate thread with the subject S7-400H, two cp441-2, put a different slave number. Best regards Min_Moderator

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