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s71200 Mbus RTU with Omron V1000 inverter

Created by: Oscar_83PL at: 10/26/2010 3:48 PM (6 Replies)

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10/26/2010 3:48 PM	Rate (0)
Oscar_83PL Bronze Member Joined: 10/22/2008 Last visit: 2/17/2025 Posts: 372 Rating: (5)	Hello, For some time it is impssible to communicate S7-1214 with RS485 module and V1000 omron invereter. Have you already tried this combination with success? Should the RTS be turned on? In inverter's manual it is said that for rs485 it should be on (rts always on)? Data to read are in 00101H so it is neccessary to give adress 101 or 40101? Any suggestion are highly recommended. best reagrds

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10/26/2010 5:13 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 3/10/2025 Posts: 15721 Rating: (2487)	I've recently worked on S7-1214C / RS-485. My first suggestion is to get the latest firmware in the PLC (1.00.02 or something like that). It corrected some issues we were having with RS485/ethernet communications. Second suggestion would be to investigate a RS485 isolator or full-duplex/half-duplex converter. The PLC RS485 module is half-duplex only and only have profibus wiring. There isn't any RTS/CTS, so you'll have to hardwire the RTS signal high (which you may be able to do with a RS485 full/half duplex converter. Can you communicate with a terminal emulator on your computer over RS485? I started out with a RS232 / RS-485 converter to verify communications parameters (baud/bits per word, etc.). Once the parameters were know, put them into the PLC program. Had the drive send out something and had the PLC watch table set to show the buffer. You will want to look at the FAQ on how to use strings with the buffer. https://support.automation.siemens.com/WW/llisapi.dll/42002283?func=ll&objId=42002284&objAction=csView&nodeid0=34612486&nodeid5=38718979&lang=en&siteid=cseus&aktprim=0&extranet=standard&viewreg=WW&load=treecontent It is also important to understand the start and end conditions for message receipt are "OR". If you know the last character appended to every message is <cr> (16#0D, Dec 13), you can put in 0D for the hex character and the software will do a much better job of pulling in message traffic one at a time. It takes some tweaking to find the right combination of start/end conditions, but it will help ignore the noise traffic (invalid packets of data). Hope this is helpful.
	science guy
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10/26/2010 5:59 PM	Rate (0)
Oscar_83PL Bronze Member Joined: 10/22/2008 Last visit: 2/17/2025 Posts: 372 Rating: (5)	I use Modbus libraries in Step Basic. If I udarstand you well you advise me to write my own library with Modbus protocol. In Siemens library I don't have any option to ingerate in modbus protocl message window. For communication it is used profibus cable and profibus connector on PLC side so there should not be any noise a problem.. Both terminating resistors are on. Is it described somewhere how PLC modbus frame look like? I am not sure if the communication frames are compatibile.

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10/26/2010 9:30 PM	Rate (0)
0_Einstein Diamond Member Joined: 7/7/2010 Last visit: 3/10/2025 Posts: 15721 Rating: (2487)	There are modbus specifications available online. As to the 00101H is the address, what is 00101H in decimal? That's the register # to use for your offset in the S7-12xx PLC's modbus read message. For example, if you want to read modbus address 40101 (decimal), the modbus address offset is 101 (decimal). To read 101 (hex), first convert to decimal (257), and tell your S7-12xx PLC to read from address 257 (decimal). Perhaps that's all you are having a problem with is the offset numerical base, you should be moving forward quickly. :) Did the modbus library automatically set up the RS485 module parameters? I still think you should verify baud, word size, parity, stop bits, etc. and after that, perhaps magic will happen for you. :)
	science guy
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10/27/2010 9:07 AM	Rate (0)
Oscar_83PL Bronze Member Joined: 10/22/2008 Last visit: 2/17/2025 Posts: 372 Rating: (5)	101 is hexal address. But what i tried was to read adress from 40001 125 bytes. So buffor should have something. What is more suprising the block Modbus_Master dont give back any error status. In inverter manual it is said that speed is in # 31(hex). So i tried to read everything from 40050 for next 100 bytes but the read buffor is all the time empty. Connection parameters are checked hudreds time so i dont think thats the problem.

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10/28/2010 11:28 AM	Rate (0)
Oscar_83PL Bronze Member Joined: 10/22/2008 Last visit: 2/17/2025 Posts: 372 Rating: (5)	The problem was solved. No matter what it is written in Omron manual just trurn off RTS in inverter option for rs485. thanks for any advice

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6/1/2016 6:37 PM	Rate (0)
IESJaume Member Joined: 5/16/2011 Last visit: 3/15/2025 Posts: 1 Rating: (0)	Hi Oscar, I'm trying to do the same program as you. I want to communicate with modbus an S7-1200 with Omron 3G3MV inverter. I would be very grateful if you sent me your program. Thank you.

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