B&B Electronics MES1B Instrukcja Użytkownika Pobierz pdf (Strona 59)

Modbus Basics

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

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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.)

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.

1 2 ... 54 55 56 57 58 59 60 61 62 63 64 ... 70 71

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B&B Electronics MES1B Instrukcja Użytkownika Strona 59