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problem with CM1241

Created by: pratik7332 at: 7/15/2014 7:01 AM (10 Replies)

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7/15/2014 7:01 AM	Rate (0)
pratik7332 Bronze Member Joined: 11/26/2009 Last visit: 10/9/2024 Posts: 222 Rating: (1)	hi, In 2 cases i have coonected weighn controler and other device for communication with modbus RTU with CPU 1214C and CM1241. The problem is somehow my data which cpu reads from device got "hang" after sometime. means its not geting updated . thnx.

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7/15/2014 2:31 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 11/14/2024 Posts: 15399 Rating: (2443)	pratik7332 hi, In 2 cases i have coonected weighn controler and other device for communication with modbus RTU with CPU 1214C and CM1241. The problem is somehow my data which cpu reads from device got "hang" after sometime. means its not geting updated . thnx. If you restart your plc, does the communications start without doing anything to the remote MB/RTU device? If you have to power cycle the plc to restore communications, you may want to look at how your plc logic handles errors and retries. Has it been working and now suddenly is not working 100% or is this a new process and has never worked 100%?
	science guy
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7/15/2014 2:43 PM	Rate (0)
pratik7332 Bronze Member Joined: 11/26/2009 Last visit: 10/9/2024 Posts: 222 Rating: (1)	thnx, the thing is ihave communicated 11 modbusdevice on the modbus RTU network using CPU 1214C by that i am geting data in 16 bit format from all the devices and it works 100%. Sometimes the data is not giving me he response when actual readings got changed means it shows the last reading. When i restart the CPU they start responding.

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7/15/2014 2:48 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 11/14/2024 Posts: 15399 Rating: (2443)	pratik7332 thnx, the thing is ihave communicated 11 modbusdevice on the modbus RTU network using CPU 1214C by that i am geting data in 16 bit format from all the devices and it works 100%. Sometimes the data is not giving me he response when actual readings got changed means it shows the last reading. When i restart the CPU they start responding. Is the problem with all 11 MB/RTU devices, or just one? If you go online with the PLC while it is in this condition, what does the MB block show for status? Are you saving the status so you can monitor it for undesirable values like errors or the worst status result that says you are triggering the MB read block even though it has not finished the current read? Maybe a screenshot of one of the problem reads while online would be helpful.
	science guy
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7/15/2014 3:07 PM	Rate (0)
pratik7332 Bronze Member Joined: 11/26/2009 Last visit: 10/9/2024 Posts: 222 Rating: (1)	hi, I will send you the Screen shot as soon as possible. the problem is with some of the RTU not all precisely out of 11 merely 2 device. The device is having display which changes the readings but i am not able to monitor it and unfortunately this things doesnt happen immediatly u can say my trends shows the flat readings sometimes. And i dont get any eror in the MB at all. I am having "BUSY" bit in the block is the only source of monitoring. Suggest me if there is anything i can do about reading proceedure.

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7/15/2014 3:24 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 11/14/2024 Posts: 15399 Rating: (2443)	pratik7332 hi, I will send you the Screen shot as soon as possible. the problem is with some of the RTU not all precisely out of 11 merely 2 device. The device is having display which changes the readings but i am not able to monitor it and unfortunately this things doesnt happen immediatly u can say my trends shows the flat readings sometimes. And i dont get any eror in the MB at all. I am having "BUSY" bit in the block is the only source of monitoring. Suggest me if there is anything i can do about reading proceedure. Not knowing exactly how your block is written, perhaps you can do like I have always done and in the remote devices toggle a bit or monitor something that is known to always be different every so often, like a clock ticker or watchdog bit. In the s7-1200 plc program, you can then monitor for the toggling. If it stops toggling, you can stop the mb/rtu for that device, restart the mb/rtu. After 3 retries you can prompt the user or take automated actions to stop the process gracefully - whichever method is appropriate. We chose 5 seconds, but for things that act quickly and could pose serious process problems, you may want to choose a smaller timeout value. As a standard approach, most siemens communications blocks give you several outputs, all of which are important. doneor new data ready (NDR)- a one-shot indicating new data is present so you can move the data from the buffer to your process DB busy - sending data -- you can monitor this busy bit with a timer and if it is busy too long, you know your communications is not working and can reset it and try again error - a one-shot you can use to reset the communications attempts and potentially alert the user and take process actions if it persists. Very good to use this to increment an error counting tag status - an integer value showing the current status of the block - save it when the error bit is true so you can look at it after the fault occurs If your block has these options, consider how to handle each of these outputs and you may find the problem.
	science guy
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7/15/2014 7:00 PM	Rate (0)
pratik7332 Bronze Member Joined: 11/26/2009 Last visit: 10/9/2024 Posts: 222 Rating: (1)	hi, I will definatly looking for the option you have mentioned it will help me in so many ways Please find out the modbus logic i have used in th program in the attached file. Guide me further for the same . Attachment modbus.pdf (223 Downloads)

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7/15/2014 7:09 PM	Rate (1)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 11/14/2024 Posts: 15399 Rating: (2443)	A couple of things I can suggest right away. The EN input should be on pretty much all the time. Just toggle the REQ input from low to high to trigger another read request. For the storage area for the read, it has been my general observation most people usea DB for the results of the read. The way I have seen the most for a 16-bit buffer in a DB would be something ugly like this: P#DB1.DBX0.0 BYTE 2 Change the DBX0.0 to DBX2.0 for the 2nd word, DBX4.0 for 3rd word, and so on. My guess is your difficulty comes from not having the EN input on constantly.
	science guy
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7/15/2014 7:19 PM	Rate (1)
William_B Posts: 5225 Rating: (1196)	...regardless of the software handling; please check also the termination (terminating resistor) of the RS485 link. w
William_B Posts: 5225 Rating: (1196)
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This contribution was helpful to 1 thankful Users 0_Einstein

7/16/2014 8:00 AM	Rate (0)
pratik7332 Bronze Member Joined: 11/26/2009 Last visit: 10/9/2024 Posts: 222 Rating: (1)	hi, Now i have enabled the EN bit with "Always high" bit,as u can see i have used MW for the storage of the data. I havent use DB for that . Thankx for help.

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