B&B Electronics MES1B Benutzerhandbuch

Manual Documentation Number: MES1A/MES1B-2106m        PN7138-rev001 

B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com 

B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com 

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Another aspect of Modbus/TCP that must be considered relates to the Unit 
ID field. Modbus/RTU incorporates the slave address field but Modbus/TCP 
replaces the slave address field with a Unit ID field. TCP/IP uses IP 
addresses to find specific nodes on the network. By using the IP address to 
specify the node, and the Unit ID to specify a Modbus/RTU device attached 
to that node, multiple slaves can be located at a single IP address. 
Unfortunately, some manufacturers of early Modbus/TCP systems assumed 
only one slave per IP address and always used a Unit ID of 00. If this early 
equipment is used, only one Modbus/RTU slave can be connected to an 
MES1A/B. (The MES1B is capable of RS-485 multidrop, allowing multiple 
slaves.) 

A few simple suggestions that may assist you if your system is experiencing 
problems include: 

•  Slow down the polling rate.  
•  Try the Disable Pipeline option in the MES1A/B configuration menu. 
•  Make sure your Modbus/TCP equipment uses sequence and Unit ID 

numbers.