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CP341 MODBUS ADDRESS MISMATCH

Created by: montu at: 9/6/2011 3:12 PM (8 Replies)

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9/6/2011 3:12 PM	Rate (0)
montu Regular Member Joined: 10/10/2008 Last visit: 3/6/2024 Posts: 24 Rating: (0)	Hi every one, I use CP341 for to communicate conzerv make energy meters data on MODBUS protocol. After completion of programming, all data are read by system. But energy consumption reading is not matched with meters displayed data. Function block used for send data: - FB8 function block used for read data:-FB7 in send data db address type on partner CPU: - "x" extended data block starting address:-F3C (hex) length: - 64(dec.). Energy reading is available on address: - 3960(dec.) also I attached MODBUS address list of energy meter. What exactly problem is possible?????? Attachment EM6400_RegisterMapDetails.tmp.pdf (808 Downloads)

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9/6/2011 7:01 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	The energy meters data in in IEEE floating point (real) format. These numbers are 32-bit in size and occupy two 16-bit modbus registers for each value. Are you taking this into account? What are the data types of the DB elements you are using to store the received data into? You have 2 options. 1) Store the data in a DB that has WORD type elements in it. Then take the two word values (registers), combine them into a DWORD using rotate / and operations, then convert the DWORD into a real. 2) Store the received data into a DB that has REAL type elements in it. This will convert the two registers directly into a REAL value for you. However, there is one caveat. You may need to swap over the registers for it to work. This is because different computers / controllers can store the numbers in different ways (high-register / low-register or low-register / high register). With 1), it is very easy to change the order of the words that make up the dword to allow for this. With 2) it is not possible, and you would have to see if the energy meter has the ability to word swap the data before it is sent (most comms interfaces that send real data have this option).
	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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9/9/2011 7:41 PM	Rate (0)
montu Regular Member Joined: 10/10/2008 Last visit: 3/6/2024 Posts: 24 Rating: (0)	Thanks smiffy, I use real data type in my DB For to storedata. So I think I don’t have to use rotate data function for actual reading. I take reading from meter and plc which are as below. Reading of meters display:-261.14956 MWH data in plc (db617.dbdw122):-2.611764e+008 (real) one other thing confused me. We have same energy meter connected with ABB plc using same MODBUS protocol. And in this system same address is used (3960) but in that case value matched in plc as well as meter. In ABB plc rotate function is used asyou suggested. So I confused very badly, and cannot abele to conclude anything.

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9/12/2011 11:21 AM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	Well it does not look as if the words are reversed as:- -261.14956 is C3829325Hex and -2.61176eE+08 is CD7913C5 Hex, but this is not for certain, as the value may be changing by very large ammount (see below). Is the value in the DB fluctuating by very large ammounts? This could be indicative of word reversal as the smaller half of the number varies a lot, and if reversed this becomes the larger half of the number, hence the large variations. So if reversed, a very small change in the Bently number would result if a very large changed to the converted number. It is possible that you might have got the address misplaced by one register such that you have the second half of one float number and the first half of the next float number. For example take the 2 numbers 10.123 and 100.456 in sucessive values in the Bently. This would equate to 4 modbus registers:- 4121 Hex, F7CF Hex, 42C8 Hex and E979 Hex (4121F7CF = 10.123 and 42C8E979 = 100.456). Now if they were reversed you would get:- F7CF4121 = -8.407237663049294e+33 and E97942C8 = -1.8833618413795425e+25. If you are misplaced by one register you would get:- F7CF42C8 = -8.407499487367603e+33 You can convert real numbers to their hexadecimal equivalents and vice versa using these on-line calculators. That way you might be able to spot what is going on by looking comparing the number you are decoding and the number in the Bently.
	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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11/21/2011 1:49 PM	Rate (0)
montu Regular Member Joined: 10/10/2008 Last visit: 3/6/2024 Posts: 24 Rating: (0)	Dear Smiffy,I have followed your suggestion. But still I do not able to achieve my goal. I mean to say still there is a difference in reading. As you said, I used two 16 bit word. But I am not able to convert that into DWORD and REAL. Kindly suggest block or any function to solve above problem.

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11/21/2011 2:35 PM	Rate (0)
Niranjan Prasad Posts: 691 Rating: (37)	Please check with your Vendor whether you have to divide the Read Value with 250/256 in the program .
Niranjan Prasad Posts: 691 Rating: (37)
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11/21/2011 4:16 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	Is it possible for you to set one of the data points in the meter to a known fixed value? If, so we can use that as a test point. If you cannot fix a value, are there any values that ar quite steady? If, so we can use that as our test point instead. Then setup you modbus to read the "test" value only (2 modbus registers) and place these 2 registers into a DB as 2 words (not a real type). This allows us to see if the data from the meter is correct, correct but needing to be reversed, or just plain wrong. For example if you set the meter value to 123.45, this decodes as 42F6E666 Hex. So the 2 modbus registers will be either 42F6 and E666 or E666 and 42F6. If it is anything else other than this, then the modbus data is just wrong for some reason.
	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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4/12/2019 8:30 AM	Rate (0)
FanaM Regular Member Joined: 10/3/2018 Last visit: 10/1/2024 Posts: 3 Rating: (0)	Good day Smiffy Thank you for the solution 1, it works perfectly and has enabled my application, of reading a floating point Modbus register provided in two separate words. I Rotate the two words to the left 16 bit, then set them to a double word, which I convert to a real and the true displayed real value is shown accurately so. Regards Fana

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5/30/2019 9:18 AM	Rate (0)
ksivam Posts: 1 Rating: (0)	Hi i am quite new and interfacing a modbus device, with same issue. i have isolated both words and see then when i swap i can get the result. i am unable to get the same results using rotate and combine, how do use the rotate and combine. Could you please post a screen shot. Thank you in advance
ksivam Posts: 1 Rating: (0)
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