B&B Electronics RT12-2222-ZP-12, RT12-4444-9T-W20, RT12-0044-ZP-12 manual Modbus Overview

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Modbus Overview

This section is written for the person who will use the RT series RTU’s with Modicon Modbus protocols for communication in Modicon programmable controller applications. It describes the different types of Modbus registers supported. The RT Series RTU’s support Modbus, Slave RTU mode.

The Modbus protocol provides the internal standard that the Modicon controllers use for parsing messages. During communications on a Modbus network, the protocol determines how each controller will know its device address, recognize a message addressed to it, determine the kind of action to be taken, and extract any data or other information contained in the message.

All of the RT series RTU’s use a common Modbus communications protocol. All data is sent and received raw units.

Engineering Note: It may be necessary to force your PLC or Modbus master device to delay between Modbus packet transmissions. Some devices transmit without a break in data packets. Because of the nature of half-duplex radio you may need to configure or program your device with a 30-50 mS delay between packets and a 1.5- 2.0 second timeout.

Modbus Data: Some Modbus devices send data differently than others. This example shows Slave address 9, using function 3 and 16. It also shows he full data address of 40001. The RT series RTU’s do not send the full address. The Modbus protocol allows a system to assume the data address based on the function type. This is true of all Modbus functions for the RT series RTU’s.

09 03 9C 40 00 01 91 7E

09 10 9C 40 00 01 02 00 00 9E 54

09 = Slave 9

03 = Read Holding Registers

9C = Starting Address High -\

40 = Starting Address Low -/ 40001

00 = Number of Points High-\

01 = Number of Points Low -/ Read 1 Point 91 = Check Sum

7e = Check Sum

Manual Documentation Number: RT-12 series-4006m

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B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104www.bb-elec.comB&B Electronics – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445www.bb-europe.com

This is an example showing what data would look like for the RT series RTUs.

09 = Slave 9

03 = Read Holding Registers

00 = Starting Address High -\

00 = Starting Address Low -/ 40001

00 = Number of Points High-\

01 = Number of Points Low -/ Read 1 Point 91 = Check Sum

7e = Check Sum

4Manual Documentation Number: RT-12 series-4006m

B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104www.bb-elec.comB&B Electronics – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445www.bb-europe.com

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Contents Wireless Modbus I/O Modules Wireless I/O Modules from B&B Electronics Table of Contents For Modbus Slave RTU mode, check and confirm the following Theory of OperationFor Peer-to-Peer mode, check and confirm the following Modbus Overview RT12-4444 Modbus Map Modbus Functions SupportedModbus Register Maps Peer to Peer Overview RT12-2222 Modbus MapTo Connect to a Controller RT12-4444-9T-W20 Front Panel IdentificationConnection Screw Terminal Description Data Activity LED Indicators Power 10.5~28 VdcLink/Sanity LED Indicators Serial RS-232 InterfaceRT12-2222-ZP-S12 Front Panel Identification RT12-4444-9T-W20 External Battery Back-upConnection Screw Terminals Description RT12-0044-ZP-S12 Front Panel Identification RT12-2222-ZP-S12 External Battery Back-upPower 10.5~28 Vdc Typical Application Peer-to-Peer RT12-0044-ZP-S12 External Battery Back-upHardware Set-up Typical Application Peer-to-Peer Typical Application Modbus Typical Application Well Monitor and Control Modbus Typical Application Well Monitor and Control Peer-to-PeerPin# Connection color Configuration Cable DescriptionTypical Application 4-20 mA to Voltage Conversion Configuration/Monitoring Software Main Configuration/Monitoring Software System MapCurrent Controller Settings Controller ConfigurationManual Documentation Number RT-12 series-4006m Master, Slave, Modbus, Peer-to-Peer Connecting / DisconnectingDigital Input Types Modbus ConfigurationRTU Alarms Analog Outputs Resting Voltage Input Voltage Alarm LimitsManual Documentation Number RT-12 series-4006m Third Party Communications Protocol Support Updating/Sending Configuration to RTUDigital Outputs Status Bar