Modbus Basics
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
Hints and Tips
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.
Manual Documentation Number: |
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph
B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353
49
