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CP 341-RS232C with Modbus master

Created by: Anit Kumar at: 4/16/2012 11:49 AM (29 Replies)

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4/19/2012 2:59 PM	Rate (0)
Anit Kumar Posts: 153 Rating: (2)	I have attached screen shot of diagnostic buffer and event id id 16#F1C8:0836 Attachment untitled.zip (193 Downloads)
Anit Kumar Posts: 153 Rating: (2)
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4/19/2012 3:08 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	Hello Anit, obviously it is a bug of the simulation software. It sends either a wrong CRC or a wrong length information. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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4/19/2012 3:14 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	Your modscan trace shows that you are getting no response from the slave device. Remember the slave will not respond at all unless it understands the request from the master, and the request is addressed to it. Are you polling the correct slave address? Your trace shows that you are polling slave adresss 222. Is 222 the slave address assigned to the PLC? Is the CP341 receiving anything? Open the instance DB for FB80. If you are using CFC, you can find the instance DB number by right clicking on the FB80 block in your CFC chart and then selecting properties. Now select open->online open and then do a refresh (press F5). This will get the lastest status of the data for FB80. Print this out using the pdf interface and post it here for me to examine.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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4/19/2012 3:27 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	smiffy Your modscan trace shows that you are getting no response from the slave device. Remember the slave will not respond at all unless it understands the request from the master, and the request is addressed to it. Are you polling the correct slave address? Your trace shows that you are polling slave adresss 222. Is 222 the slave address assigned to the PLC? Is the CP341 receiving anything? Open the instance DB for FB80. If you are using CFC, you can find the instance DB number by right clicking on the FB80 block in your CFC chart and then selecting properties. Now select open->online open and then do a refresh (press F5). This will get the lastest status of the data for FB80. Print this out using the pdf interface and post it here for me to examine. Well smiffy, when the diagnostic buffer shows 0836 a wrong CRC was received. Or do you think this is an old entry? When the CP receives a wrong CRC it won't answer. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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4/19/2012 4:06 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	Ah sorry, I didn't notice the error code post. Yes you are correct a invalid CRC will also cause the slave to ignore the request. I asked for the contents instance DB as that looks to have a data receive buffer in it (the empfang.register array). This array is 128 words in length, which equates to 256 bytes, which just happens to be the maximum data size for a request. So I reckon this might be where the receive packet data is stored by the P_RCV_RK FB. If it is, the contents would tell us what the CP341 received, which would be very helpful in determining what is going wrong. I might be wrong and this array could be for some other data, but it is worth a try. If this does not yeild the recive packet data, we would have to use some for of packet data capture program on the PC (something like serial port monitor).
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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4/19/2012 4:26 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	smiffy I asked for the contents instance DB as that looks to have a data receive buffer in it (the empfang.register array). This array is 128 words in length, which equates to 256 bytes, which just happens to be the maximum data size for a request. So I reckon this might be where the receive packet data is stored by the P_RCV_RK FB. Hello Smiffy, as far as I know the receive buffer of FB80 is only used with bit oriented functions. Register read/write is carried out directly by P_SND_RK / P_RCV_RK. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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4/20/2012 7:33 AM	Rate (0)
Anit Kumar Posts: 153 Rating: (2)	hello smiffy, I have attached screen shots of instant DB with and with out polling from mod scan32. My slave id is 222, parity = even, stopbit=1 and cable connection of cp and cpu as: cp cpu 2 = 3 3 = 2 5 = 5 please solve my problem where I am wrong???? Attachment instant_db.zip (180 Downloads)
Anit Kumar Posts: 153 Rating: (2)
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4/20/2012 11:05 AM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	Kaulquappe Hello Anit, obviously it is a bug of the simulation software. It sends either a wrong CRC or a wrong length information. Regards, Kaulquappe Kaulquappe, I don't think it is. I have used modscan many times and have never had a issue with it. You can see from the transmitted data that the request is indeed correct:- The poll is shown as: 222,004,000,000,000,020,227,106 This decodes as, slave address 222, function code 04, start offset 0 (modbus address 30001), number of data points 20. I have checked the CRC and it is also correct. So the poll looks good on the master side (provided it is sending what it says it is, which I have no doubts that it is). Kaulquappe Hello Smiffy, as far as I know the receive buffer of FB80 is only used with bit oriented functions. Register read/write is carried out directly by P_SND_RK / P_RCV_RK. Regards, Kaulquappe Alas, it seems that you are correct. I broke the FB80 block protection and had a peek at the internals, and it seems that it does not use the "empfang.register" for the received data. This is what the instance DB print out also confirms. However, I also noticed in the CP daignostic that there are framing errors being detected. This would certainly lead to the slave not being able to decode the request correctly. Anit, are you certain that you have setup your serial interface parameters correctly? They must be IDENTICAL between master and slave.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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4/21/2012 5:47 AM	Rate (0)
Anit Kumar Posts: 153 Rating: (2)	hello smiffy, Kaulquappe Now my system is running good as well as with modscan and also with another modbus master system. I were making correct parameter setting as you guys discussed. I found some fault in my serial cable , I removed old connectors and placed new connectors only. Anyways thanks a lot.......keep it up
Anit Kumar Posts: 153 Rating: (2)
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This contribution was helpful to 3 thankful Users smiffy Kaulquappe TIBI68

3/24/2013 10:05 AM	Rate (0)
Chandra Tiwari Posts: 247 Rating: (2)	Hi Smiffy, I am using SND_341 (FB 120) and RCV_341 (FB 121) in PCS7 V8.0 up 1 project. I dont know the subnet1 id and subnet2 id. I also want to do modbus redundancy in my project i am using 2 modbus cards for loop in and loop out connected with several relay devices on modbus RS485.
Chandra Tiwari Posts: 247 Rating: (2)
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