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S7 1200 Modbus RTU_ MB_Master Busy

Created by: kaarthikeyan at: 10/29/2013 8:49 AM (8 Replies)

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10/29/2013 8:49 AM	Rate (0)
kaarthikeyan Posts: 5 Rating: (0)	Dear Experts, I have typical problem in S7 1200 modbus communication. I am using TIA V11 SP 2 software and CPU 1212 , CM 1241 (RS 485) module to communicate a Flow meter(Slave). Communication settings : Baud Rate :9600 (4800 option), stop bit :1, parity: none, slave ID : 1,data bits 8. i used MB_Master in S7 1200 PLC. when ever Req is triggred TX and RXis blinking in CM module but in MB_Master is showing Busy status not getting data.I used port monitor software to check the communication. I can see master telegram and salve response(after 3.5 bit time)butS7 1200 PLC is notshowing the received values.I am attaching my program for your reference. THis flow meter is communicating with S7 200 modbus.Many times i used S7 1200 for Modbus communication. Kindly help me solve the issue. i am attaching my program with this mail.Regards, Karthi. Attachment MOdbus_485_tex_CM485.zip (978 Downloads)
kaarthikeyan Posts: 5 Rating: (0)
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10/30/2013 8:29 AM	Rate (0)
Fafner Silver Member Joined: 3/20/2013 Last visit: 4/3/2024 Posts: 676 Rating: (44)	With a short look over your project the call of the modbus FB look alright. Are you only getting the BUSY flag of your FB or do you also get any error messages? (I guess you already triggered the ERROR bit of the FB MB_Master to save the STATUS in case of an error?) Do you have any more approach to your communication problem? Best regards, Fafner
	Best Regards, Fafner
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This contribution was helpful to 1 thankful Users Tomy Master

10/30/2013 11:10 AM	Rate (0)
kaarthikeyan Posts: 5 Rating: (0)	Dear Fafner, I am not getting any error in the MB_Master block. But while looking for the cause i note in MB_MasterDB particularly at RCV_PTP selection i can see some value.I feel this value is RCV error. I am attaching the screen shot of the DB and port monitor which shows the reply of Slave(this may not match start address or data length in project i have taken it while trying diffrent combinations). Kindly have a look. Regards, karthi Attachment C:\Documents and Settings\IN218080\Desktop\Screen Shot.zip (983 Downloads)
kaarthikeyan Posts: 5 Rating: (0)
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8/7/2015 9:12 AM	Rate (0)
Ibrahim Nassar Posts: 1 Rating: (0)	Hi , Did anybody find a solution for that problem ? I have the same problem : Trying to communicate with Flow transmitter ( From SIEMENS) using CM1241 module ; always the MASTER BLOCK is showing busy . Also I cannot find the 1CH32 model in the V12 catalog. Please help me. Thanks :)
Ibrahim Nassar Posts: 1 Rating: (0)
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9/13/2015 5:16 PM	Rate (0)
dontnv Posts: 5 Rating: (0)	Dear kaarthikeyan and all Did you FIND a solution for your problem? I have same problem now. Sometime I only getting the BUSY flag, not getting DONE or ERROR flag or any messages. But if I STOP and then RUN PLC then everything seem like OK.
dontnv Posts: 5 Rating: (0)
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12/3/2015 10:30 AM	Rate (0)
Mahesh N Bronze Member Joined: 10/3/2013 Last visit: 9/14/2024 Posts: 125 Rating: (3)	Dear All, Please use trigger pulse for request in parameter ("REQ"). for continuous operation use 1sec. pulse or write logic on don bit. This will be work. Regards, Mahesh N

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11/13/2019 2:01 PM	Rate (0)
C-3PO Bronze Member Joined: 5/30/2014 Last visit: 11/6/2024 Posts: 150 Rating: (18)	Hello, I had a similar problem and solution was to change MODBUS library, like in this post: https://support.industry.siemens.com/tf//ww/en/posts/modbus-rtu-status-7000/147378/?page=0&pageSize=10 MODBUS RTU didn't worked, but old MODBUS worked!
	If you find my contribution helpful please RATE it :))
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11/14/2019 9:00 AM	Rate (0)
Duris_I Diamond Expert Joined: 4/28/2015 Last visit: 11/16/2024 Posts: 10614 Rating: (828)	Hello, pls check your CPU firmware and version, due this you need use specific library, all is described inside TIA (your version) system manual.
	With best regards... Ivan Duris Flight: OMICO
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11/14/2019 9:41 AM	Rate (0)
JKV JAMES ❤️(Köni... Silver Member Joined: 12/27/2018 Last visit: 10/2/2024 Posts: 510 Rating: (43)	I got a similar problem while I was commissioning a program for rig ROWAN EXL in sept 2018. The issue was Modubus busy for long time.Later the CM1241 Communication LED go off from blinking( modbus communication lost). It will work one or two days normally then go off. I found a solution and rectified it by editing the program and now its working satisfactory. Its easy. Change program like below this in each steps REQ=0 (Reset REQ) So it don't allow pointer to BUSY for long time, CPU will cancel request immediately and call for new value in other registry.It will work check it. Refer the attachment program screenshot. refer modbus_4.jpeg ENJOY!!! Attachment modus_james.zip (866 Downloads)
	Last edited by: JKV JAMES at: 11/14/2019 09:47:44 Last edited by: JKV JAMES at: 11/14/2019 09:52:28 Jinson James, M.Tech (Power Electronics and Power System),
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