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Modbus RTU extended range input register

Created by: david1305 at: 7/8/2013 4:36 PM (12 Replies)

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7/8/2013 4:36 PM	Rate (0)
david1305 Posts: 4 Rating: (0)	Hi all, I'm trying to read from extended range input register 311023 on a Schneider Relay with no success. This works for holding registers (e.g. 413033) but not for input registers. Is there a way around this? I've tried reading from 311023using CAS Modbus Scanner and it works fine so I've a feeling its just the Siemens MB_MASTER block not allowing this.
david1305 Posts: 4 Rating: (0)
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7/8/2013 5:02 PM	Rate (0)
William_B Posts: 5225 Rating: (1202)	david1305 Hi all, I'm trying to read from extended range input register 311023 on a Schneider Relay with no success. This works for holding registers (e.g. 413033) but not for input registers. Is there a way around this? I've tried reading from 311023using CAS Modbus Scanner and it works fine so I've a feeling its just the Siemens MB_MASTER block not allowing this. Hi-ya, I will not pretend that I know your particular device.. maybe I have an alternative solution. Many of these devices make it possible to buffer "user monitor" values to a register. Some has up to 10 registers you can set for this purpose. My 2c. w
William_B Posts: 5225 Rating: (1202)
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7/12/2013 10:22 AM	Rate (0)
david1305 Posts: 4 Rating: (0)	Hi William, Thanks for your reply! You are absoloutely correct that I can map addresses to a more readable MODBUS address. Unfortunately, I need to read about 100 variables which is far more than I can access using that method. I was just using the address mentioned above as one example.
david1305 Posts: 4 Rating: (0)
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7/12/2013 12:32 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	david1305 I've tried reading from 311023using CAS Modbus Scanner and it works fine so I've a feeling its just the Siemens MB_MASTER block not allowing this. Hello David, you are right, the MBMASTER block doesn't support this address. It is a shame that a lot of manufacturers don't keep close to the Modbus specification and use the addressing of the data link layer but keep that oldfashioned addressing of the application layer. Unfortunately Siemens turned back to that old stuff with S7-1200. S7-300 and S7-400 are capable to execute this addresses. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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7/12/2013 1:15 PM	Rate (0)
William_B Posts: 5225 Rating: (1202)	Open question.. If the standard library is not up to the task, it should be possible to develop it. Would there be somewhere (like http://www.oscat.de) be published some coding that makes a serial port Modbus RTU capable? Re-inventing the wheel should not be required. David.. is it a must that you use all those variable or have to use an S7-1200? I think there are "converters" available that can port those addresses to whichever protocol and memory you require. You are looking for a Modbus-to-modbus converter.. shifting the memory space. Sounds good in theory.. but I doubt it is too much helpful. Sorry that is all I have to bring to the party. w
William_B Posts: 5225 Rating: (1202)
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7/12/2013 1:29 PM	Rate (0)
david1305 Posts: 4 Rating: (0)	Thanks for the help. I think I'll pick the most important data and see if the customer is satisfied. If not, I'll buy a Modbus RTU to Modbus TCP/IP gateway and read the data to the S7-1200 that way.
david1305 Posts: 4 Rating: (0)
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7/12/2013 1:35 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	david1305 I think I'll pick the most important data and see if the customer is satisfied. If not, I'll buy a Modbus RTU to Modbus TCP/IP gateway and read the data to the S7-1200 that way. Well David, that won't solve your problem, as the ModbusTCP blocks of S7-1200 have got the same address range. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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7/12/2013 1:56 PM	Rate (0)
William_B Posts: 5225 Rating: (1202)	Well David, that won't solve your problem, as the ModbusTCP blocks of S7-1200 have got the same address range. Regards, Kaulquappe There are some of these gateways that can re-address what comes in. The advantage is that you can cosolidate random pieces of addresses into a single block. ..but what I say here now is on theoretical level as I have not used that before. As these products are not Siemens products I will not advertise the manufacturers/distributers. Random question.. How easy would it be to use a micro-controller as "translator"? I have seen someone publish coding for the Ardiuno for Modbus protocol. how much of the standard he ha put into coding, I am not 100% sure.. but from my studies it seems to be uch of it. Ideas from someone else maybe? w
William_B Posts: 5225 Rating: (1202)	Last edited by: William B. at: 7/12/2013 1:56 PM
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7/12/2013 2:36 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 3/10/2025 Posts: 1557 Rating: (540)	William B. There are some of these gateways that can re-address what comes in. Like this one for example. I have used this to remap input registers to holding registers so a master device that could only user function codes 03 & 16 could read input regisers from a slave device. I cannot confirm whether it will support extended registers as the documentation doesn't say that it does (it also doesn't say that is doesn't either so it might be possible).
	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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7/12/2013 2:55 PM	Rate (0)
TIBI68 Gold Member Joined: 12/1/2009 Last visit: 2/9/2025 Posts: 672 Rating: (147)	Hi david1305 , are you only reading data? Youcan build the modbus request frame yourself and send it to the device. I dont see any problem in that. In receiving theanswer frame you need to calculate the CRC before transferringthe data into your S7-destination addresses. That's it.
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