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Tips for Modbus

Created by: Denilson Pegaia at: 8/24/2009 5:45 PM (11 Replies)

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12 Entries

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8/24/2009 5:45 PM	Rate (4)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 4/4/2025 Posts: 4406 Rating: (1480)	General Tip; 1 - Use the first scan bit (e.g. M1.0)to call the configuration block (MB_COMM_LOAD). The MD_Master / MB_Slave could be called at any scan. 2 - The configuration done by MB_COMM_LOAD, overwrite the "Device configuration" settings. So the parameter of "Device configuration" e.g. doesn't matter. 3 - For RS485: RS On Delay and RS Off Delay has no significance. 4 - Compared with S7-200 = Delay Parameter has the same meaning. RESP_TO (S7-1200) = Time out (S7-200) There is more information avaliable at the FAQ "How do you establish MODBUS-RTU communication with STEP 7(TIA PORTAL)V11 for the SIMATIC S7-1200?" http://support.automation.siemens.com/WW/view/en/47756141
	Last edited by: Pegaia at: 8/16/2012 3:57 PM Actuallizing of FAQ name. Last edited by: Pegaia at: 1/6/2011 11:29 AM link FAQ Last edited by: Pegaia at: 10/1/2010 12:36 PM new points 2,3,4 Denilson Pegaia Siemens Industry Sector Technical Support
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This contribution was helpful to 8 thankful Users Tomy Master Out Control Philip_BE SRITN iNano lmunoz jnthchica asamen7

8/25/2009 11:42 AM	Rate (0)
Robster Gold Expert Joined: 5/28/2008 Last visit: 4/4/2025 Posts: 1343 Rating: (141)	All Outputs at MB_MASTER or MB_Slave are only avaible during using this block. To see e.g. a status, you have to save them into another datablock or MW. MB_MASTER try to send a telegram 3 times, with a break of configurated RESP_TO at MB_COMM_LOAD. After 3 failures, you get a timeout.

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8/25/2009 2:46 PM	Rate (1)
bakerjw Posts: 126 Rating: (18)	Make sure that M1.0 is set up for the PLC under device configuration - System and Clock Memory. Enable the use of the system memory byte must be checked. It was not clearly stated in the manual but MB_COMM_LOAD needs to be executed a single time to configure the serial port and pass information to either the MB_MASTER or MB_SLAVE function block. The output pins and words of the MB_MASTER or MB_SLAVE function blocks are valid only for a single scan. As robster stated, in order to capture an error code, it is simplest to use a NO contact with the error bit and move the error code to a MW location. See the attached example. The REQ input of MB_MASTER is also a pulsed input. Attachment MB_Master_Example.JPG (3006 Downloads)
bakerjw Posts: 126 Rating: (18)
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This contribution was helpful to 4 thankful Users Tomy Master Seattle Mark lmunoz nhuhau

7/2/2010 8:02 PM	Rate (1)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 4/4/2025 Posts: 4406 Rating: (1480)	Hi, Here there is a sample program to comunicate S7-1200 wit Modsim (as Modbus simulation slave). Attachment ModBus Master RS232.zip (2260 Downloads)
	Denilson Pegaia Siemens Industry Sector Technical Support
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7/2/2010 8:04 PM	Rate (2)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 4/4/2025 Posts: 4406 Rating: (1480)	And here, there is the Printscreens of the open project Attachment S7 1200 RS232 ModBus Forum.zip (2261 Downloads)
	Denilson Pegaia Siemens Industry Sector Technical Support
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This contribution was helpful to 2 thankful Users Tranhieu0983 AChmiel

8/6/2010 3:46 PM	Rate (1)
MrPaiva Silver Member Joined: 6/29/2010 Last visit: 10/27/2022 Posts: 112 Rating: (63)	Hi to all. Only for information... The example posted by Pegaia uses the RS232 module. The RS232 module is used for point-to-point communication, for network communication (maximum of 32 devices in the same network without repeater) in Modbus-RTU, the RS485 module have to used.

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This contribution was helpful to 1 thankful Users Denilson Pegaia

10/25/2012 8:03 PM	Rate (0)
lmunoz Posts: 2 Rating: (0)	See how I can change the data type in where it says MB_DB MB_COMM_LOAD_DB to Variant Me despido Atte. Luis Muñoz.
lmunoz Posts: 2 Rating: (0)
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11/27/2012 11:02 AM	Rate (0)
Philip_BE Posts: 6 Rating: (0)	Easy tools for testing modbus connections: (TCP & RTU) http://www.win-tech.com/html/demos.htm I used the modscan32 tool for simulating the modbus client (or master). Modsim can be used for simulating the server (or slave) device. Note: the trail versions have a limited connection time, but for testing applications it's OK. Best regards
Philip_BE Posts: 6 Rating: (0)	Last edited by: Philip_BE at: 11/27/2012 11:06 AM
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10/7/2013 8:39 AM	Rate (0)
O_Moderator Diamond Member Joined: 4/24/2009 Last visit: 8/20/2024 Posts: 2682 Rating: (135)	New questions splitted to read and write data to drive through modbus communication (RS-485) from Siemens PLC S7-224XP Modbus communication between S7-1200 plc,CM1241 Module and ABB VFD ACS550 Drive Best regards O_Moderator
	Tips&Tricks for the forum usage
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7/27/2014 10:02 PM	Rate (0)
Out Control Posts: 204 Rating: (1)	Pegaia 2 - The configuration done by MB_COMM_LOAD, overwrite the "Device configuration" settings. So the parameter of "Device configuration" e.g. doesn't matter. Dear when i configure MB_COMM_LOAD that didn't overwrite in device configuration setting ...are this is a problem in my program becouse i find miss connection between PLC and slave Regards
Out Control Posts: 204 Rating: (1)
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