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Summary of Contents for RS485 Modbus adapter

Page 1: ...RS485 Modbus adapter for RVT Touchscreen Installation and start up guide ...

Page 2: ...chnical data 11 4 5 Commissioning process 12 4 6 To set the COMMUNICATION LOCK parameter 13 4 7 To test the communication 13 5 Modbus protocol overview 14 5 1 Overview 14 5 1 1 Transactions on Modbus Networks 14 5 1 2 Serial Transmission Mode 14 5 2 Data Addresses in Modbus Messages 15 5 3 Supported function codes 15 6 Data access 16 6 1 Access levels 16 6 2 Minimum and maximum values 16 6 3 Modbu...

Page 3: ...RS 485 Table of contents 3 8 2 References 22 8 3 Adequate choice of an RS232 RS485 converter at the computer side 22 Contact us 24 ...

Page 4: ...to the RVT Installation and operating Instructions to get the sufficient knowledge To know more about the RVT data access please refer to the RVT Modbus data table As other devices may be connected through the RS485 Modbus adapter the term controller will be used here to define the device 1 3 How to use this manual Chapter 2 is a short description of the Modbus adapter Chapter 3 contains a descrip...

Page 5: ...Factor Controller RVT Touchscreen which enables the connection of the RVT to a Modbus system The controller is considered as a slave unit in the Modbus network Through the Modbus adapter it is possible to Read measurements and logged values Read and write parameters settings of the controller Activate output relays Read status information Read device identification and type numbers 2 3 Compatibili...

Page 6: ...ce can be achieved by splitting the devices from one port onto two ports 3 1 Communication mode MODBUS protocol uses half duplex communications regardless of the hardware Half duplex hardware shares the same lines for transmit and receive whereas full duplex hardware has dedicated transmit and receive lines 3 2 SINGLE ENDED versus DIFFERENTIAL data transmission Single ended transmission is perform...

Page 7: ...B output terminals and will have a signal ground C connection Although proper connection to the signal ground is important it isn t used by a differential line receiver in determining the logic state of the data line A differential line receiver senses the voltage state of the transmission line across two signal input lines A and B It will also have a signal ground C that is necessary in making th...

Page 8: ...nd only generally at the Modbus Master side The shield is not to be used as a signal common or ground The table below lists typical cable recommendations RS 232 Up to 15m 50ft virtually any standard shielded twisted pair with drain Belden 9502 or equivalent RS 422 and RS 485 Up to 1200m 4000ft 24 AWG twisted pair with foil shield and drain wire on each pair Belden 9841 for 2 wire and 9729 for 4 wi...

Page 9: ...s 9 Various kind of RS485 to RS232 converters exists To bridge the Modbus network to another kind of software protocol various kinds of protocol converters may be used They are often called protocol gateway Modbus to Profibus Ethernet CAN ...

Page 10: ...plied on the RS485 network Advantage no ground loop The adapter has an integrated terminator resistance which may be connected with a switch Advantage no external device to be added The adapter contains transient voltage suppressors Advantage the device and the network are protected against voltage surges The adapter is fitted with transmission and reception indication LED s Advantage it allows vi...

Page 11: ...t temperature 20 to 70 C Number of nodes Tx drive 32 max Rx loading receiver impedance is 1 unit load per RS485 Modbus adapter Size of the Link 247 stations including repeaters 31 stations and 1 repeater per segment Medium Shielded twisted pair RS485 cable Belden 9841 typical Maximum Bus Length 1200 m Topology Multi drop Serial Communication Type Asynchronous 2 wires half Duplex Baud rate 110 300 ...

Page 12: ...vided in the Modbus data table 4 5 Commissioning process To install the RS485 Modbus adapter follow the hereafter commissioning process Disconnect power supply from the controller Wait the required time to ensure all capacitors are discharged Connect the signal ground if present to GND Connect the twisted pair to the A and B connections Insert the RS485 Modbus adapter in the controller Fix it with...

Page 13: ...ee the trouble shooting section hereafter 4 6 To set the COMMUNICATION LOCK parameter If the RVT s parameters should be changed only from the Modbus network set the Communication lock item as locked It can be found under the following menu o COMMUNICATION I O CONFIGURATION COM SETTINGS Set the Communication lock parameter to Locked 4 7 To test the communication Depending on the way the controller ...

Page 14: ...ng the action requested in the query Typical master devices include host processors and programming panels Typical slaves include programmable controllers The master can address individual slaves or can initiate a broadcast message to all slaves Slaves return a message called a response to queries that are addressed to them individually Responses are not returned to broadcast queries from the mast...

Page 15: ...tus of discrete inputs 3 Read Holding Registers 4XXXX Reads contents of output registers 4 Read Input Registers 3XXXX Reads contents of input registers 5 Force Single Coil 0XXXX Sets the status of a discrete output 6 Preset Single Register 4XXXX Sets the value of a holding register 7 Read Exception Status Device specific see Modbus data table of a device 8 Diagnostics Checks the communication syst...

Page 16: ...imum allowable values the variable will be overridden with its minimum or maximum value An ILLEGAL DATA VALUE exception error is sent back See the Modbus data table for more details 6 3 Modbus Data table Data are arranged in several tables for convenience Individual tables contain similar information Table data may be read only or read write access Data in each table is pointed to in a Modbus comm...

Page 17: ...ers or SCADA systems is intended to use Modbus devices to perform a measurement control or logging function It often provides tools for quick configuration of known types of instrument Such packages make it easy for a user to start a system without needing to know Modbus commands but may not provide the tools for a commissioning engineer to diagnose problems when a system does not respond as antic...

Page 18: ...he register addresses To ensure that a read or write message to a Modbus address will produce a normal response check that the register address corresponds exactly to the desired data requested In Modbus register addressing there are several categories of register including holding registers numbered from 40001 upwards and input registers numbered from 30001 upwards The category of register addres...

Page 19: ...es Fetch comm event log function 12 to look at the history of errors Diagnostics function and subfunctions function 8 Loopback diagnostics subfunction 0 returns a response identical to the query Restart communication subfunction 1 Force Listen only mode subfunction 4 Read various diagnostic counters 7 8 Debugging tool and documents The user can find much application on the internet to scan Modbus ...

Page 20: ...ssage block CTS ClearToSend hardware handshaking signal Used with RequestToSend Earth or Earth Ground Global zero voltage reference point Physical connection is made to the earth through a grounding rod water pipe or other reliable connection Ground Voltage reference point of a circuit It may or may not be connected to earth ground though it is generally assumed to be at zero volts Sometimes used ...

Page 21: ...client applications OPC is a concept agreed upon by a committee of members from the OPC foundation Most automation companies in the market place including ABB are members of this foundation OPC uses state of the art technologies like COM DCOM ActiveX of Microsoft and makes development and programming easier In the OPC world there are two major types of applications OPC Servers and OPC Clients OPC ...

Page 22: ...oftware implementation of data flow control 8 2 References Modbus Data Table RVT Modbus Data Table for the RVT RVT Installation and Operating Instructions Modicon Modbus Protocol Reference Guide PI MBUS 300 Rev J 8 3 Adequate choice of an RS232 RS485 converter at the computer side In a RS 485 network a control of the direction is needed to alternate between transmission and reception Two cases may...

Page 23: ...he Modbus slave and no answer will be initiated If RTS is released too late the answer will not be received completely by the Modbus master As a consequence to ensure higher throughput and reliable communication the recommendation is done to choose an RS 232 RS 485 able to sense and manage the data direction and to avoid any computer dependent flow control Missing to do so may lead to force the us...

Page 24: ... Products Avenue Centrale 10 Zoning Industriel de Jumet B 6040 Charleroi Jumet Belgium Phone 32 0 71 250 811 Fax 32 0 71 344 007 E Mail Power Quality be abb com www abb com lowvoltage C opyright 2011 AB B 2G C S 215013A0050 J une 2011 ...

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