BECKHOFF BC7300 User Manual

MODBUS Bus Terminal Controller BC7300

Version: 1.5 Last change: 2006-11-06

Please note the following

Target group

Safety requirements

The documentation has been prepared with care. The products described

This description is only intended for the use of trained specialists in control and automation engineering who are familiar with the applicable national standards.

The responsible staff must ensure that the application or use of the products described satisfy all the requirements for safety, including all the relevant laws, regulations, guidelines and standards.

are, however, constantly under development. For that reason the documentation is not in every case checked for consistency with performance data, standards or other characteristics, and does not represent an assurance of characteristics in the sense of § 459, Para. 2 of the German Civil Code. In the event that it contains technical or editorial errors, we retain the right to make alterations at any time and without warning. No claims for the modification of products that have already been supplied may be made on the basis of the data, diagrams and descriptions in this documentation.

This manual is copyrighted. Any reproduction or third party use of this protected publication, whether in whole or in part, without the written permission of Elektro Beckhoff GmbH, is forbidden.

BC7300

Table of contents

1. Foreword 5

Notes on the documentation 5

Liability Conditions 5 Delivery conditions 5 Copyright 5

Safety Instructions 6

State at Delivery 6 Description of safety symbols 6

Table of contents

2. Basic Principles 7

Device Description of the BC7300 7 The Beckhoff Bus Terminal System 7 The interfaces 9

Electrical power supply 9 Power contacts feeding points 9 Power contacts 9 Fieldbus connection 9 Configuration and programming interface 10 KS2000 Software 10 TwinCAT BC 10 K-Bus Contacts 10 Electrical isolation 10

Operating Modes of the Bus Terminal Controller 11 Mechanical structure 11 Technical data 14 Peripheral Data in the Process Image 15 Start-up procedure and Diagnostics 16 Fieldbus errors 18

3. MODBUS 19

Basic Principles 19 Bus Topology 19 Process Data and Memory Map 20

MODBUS Process Image 22 BC7300 Process Image 22 Assignment of the Bus Terminals 23

Setting and Parameterisation of the MODBUS 24

Parameterisation Table 25

The MODBUS Protocol 26

ASCII 26 RTU 26

Functions 27

Read Digital Outputs (Function 1) 27 Read Digital Inputs (Function 2) 28 Read Analog In/Outputs (Function 3) 28 Read Analog Inputs (Function 4) 29 Writing a Digital Output (Function 5) 30 Writing an Analog Output (Function 6) 30 Writing a Number of Digital Outputs (Function 15) 31 Writing a Number of Analog Outputs (Function 16) 32 Writing and Reading Analog Outputs and Inputs 33 (Function 23) 33 Echoes a query (Sub-Function 0) 35 Bus Coupler Reset (Sub-Function 1) 35 Delete All Counter Contents (Sub-Function 10) 35 Bus Communication Error Counter (Sub-Function 11) 35 Error Answer Counter (Sub-Function 13) 35 Slave Answers (Sub-Function 14) 36

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Table of contents

Unsent Slave Answers (Sub-Function 15) 36 Number of Error Answers (Sub-Function 16) 36

BC7300 Error Answers 37

4. Bus Terminal Controller 38

PLC Cycle Time 38 PLC Variables 38 Remanent Variables 38

Persistent Data 39

Allocated flags area 40

5. Appendix 41

MODBUS Interface 41 Mapping the Bus Terminals 42 List of references 42 Firmware 42

Table 42

Example Program 43

Explanation of the Program 43 The Program in the Bus Terminal Controller 43 Creating the BOOT Program 44 MODBUS Communication 44

6. Questions and Answers 46

General 46

No communication with the BC7300 46 Mapping of the digital and the byte-oriented Bus Terminals onto a fixed address 46 Drop of the digital outputs 46

7. Index 47

8. Support and Service 48

Support and Service 48

Beckhoff Headquarters 48

Beckhoff's branch offices and representatives 48

4 BC7300

Foreword

Notes on the documentation

This description is only intended for the use of trained specialists in control and automation engineering who are familiar with the applicable national standards. It is essential that the following notes and explanations are followed when installing and commissioning these components.

Liability Conditions

The documentation has been prepared with care. The products described are, however, constantly under development. For that reason the documentation is not in every case checked for consistency with performance data, standards or other characteristics. None of the statements of this manual represents a guarantee (Garantie) in the meaning of § 443 BGB of the German Civil Code or a statement about the contractually expected fitness for a particular purpose in the meaning of § 434 par. 1 sentence 1 BGB. In the event that it contains technical or editorial errors, we retain the right to make alterations at any time and without warning. No claims for the modification of products that have already been supplied may be made on the basis of the data, diagrams and descriptions in this documentation.

Delivery conditions

In addition, the general delivery conditions of the company Beckhoff Automation GmbH apply.

This documentation is copyrighted. Any reproduction or third party use of this publication, whether in

whole or in part, without the written permission of Beckhoff Automation GmbH, is forbidden.

BC7300 5

Foreword

Safety Instructions

State at Delivery

All the components are supplied in particular hardware and software configurations appropriate for the application. Modifications to hardware or software configurations other than those described in the documentation are not permitted, and nullify the liability of Beckhoff Automation GmbH.

Description of safety symbols

The following safety symbols are used in this documentation. They are intended to alert the reader to the associated safety instructions..

This symbol is intended to highlight risks for the life or health of personnel.

Danger

This symbol is intended to highlight risks for equipment, materials or the

Attention

environment.

This symbol indicates information that contributes to better understanding.

Note

BC7300 6

Basic Principles

Up to 64 Bus Terminals

Each having 2 I/O channels for each signal form

De-centralised wiring of each I/O level

IPC as controller

Bus Couplers for all usual bus systems

Standard C - rail assembly

Modularity

Device Description of the BC7300

The BC7300 Bus Terminal Controller is a Bus Coupler with integrated PLC functionality and a MODBUS slave interface. The controller is programmed in IEC 1131-3. Up to 64 terminals belonging to the Beckhoff Bus Terminal System can be connected to the BC7300. These include analog signal types for current and voltage, as well as PT100 and thermocouples, in addition to digital input and output terminals. The Bus Terminal Controller's MODBUS interface allows a MODBUS master to be connected.

The Beckhoff Bus Terminal System

The Bus Terminal system is the universal interface between a fieldbus system and the sensor / actuator level. A unit consists of a Bus Coupler as the head station, and up to 64 electronic series terminals, the last one being an end terminal. For each technical signal form, terminals are available each having two I/O channels, and these can be mixed in any order. All the terminal types have the same mechanical construction, so that difficulties of planning and design are minimised. The height and depth match the dimensions of compact terminal boxes.

Fieldbus technology allows more compact forms of controller to be used. The I/O level does not have to be brought to the controller. The sensors and actuators can be wired de-centrally, using minimum cable lengths. You can locate the controller installation anywhere within the plant. The use of an Industrial PC as the controller means that the operating and observing element can be implemented in the controller’s hardware. The controller can therefore be located at an operating panel, in a control room, or at some similar place. The Bus Terminals form the de-centralised input/output level of the controller in the control cabinet and the subsidiary terminal boxes. The power sector of the plant is also controlled over the bus system in addition to the sensor/actuator level. The Bus Terminal replaces the conventional series terminal as the wiring level in the control cabinet. The control cabinet can have smaller dimensions.

The Beckhoff Bus Terminal system unites the advantages of a bus system with the possibilities of the compact series terminal. Bus Terminals can be driven within all the usual bus systems, thus reducing the controller parts count. The Bus Terminals then behave like conventional connections for that bus system. All the performance features of the particular bus system are supported.

The easy, space-saving assembly on a standard C-rail, and the direct wiring of actuators and sensors without cross-connections between the terminals standardises the installation. The consistent labelling scheme also contributes.

The small physical size and the great flexibility of the Bus Terminal system allows it to be used wherever a series terminal is also used. Every type of connection, such as analog, digital, serial or the direct connection of sensors can be implemented.

The modular assembly of the terminal strip with Bus Terminals of various functions limits the number of unused channels to a maximum of one per function. The presence of two channels in one terminal is the optimum compromise of unused channels and the cost of each channel. The possibility of galvanic isolation through potential feed terminals also helps

Basic Principles

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Basic Principles

End Terminal

Potential

contacts

Bus Coupler

Display of the channel state

K-Bus

End terminal

Potential feed terminals for galvanically isolated groups

The principle of the Bus Terminal

to keep the number of unused channels low.

The integrated LEDs show the state of each channel at a location close to the sensors and actuators.

The K-Bus is the data path within a terminal strip. The K-Bus is led through from the Bus Coupler through all the terminals via six contacts on the terminals‘ side walls. The end terminal terminates the K-Bus. The user does not have to learn anything about the function of the K-Bus or about the internal workings of the terminals and the Bus Coupler. Many software tools that can be supplied make project planning, configuration and operation easy.

The operating voltage is passed on to following terminals via three power contacts. You can divide the terminal strip into arbitrary galvanically isolated groups by means of potential feed terminals. The feed terminals play no part in the control of the terminals, and can be inserted at any points within the terminal strip.

Up to 64 terminals may be located in a terminal strip, including the potential feed terminals and end terminal.

Bus Coupler BC7300

power supply

input terminal

K-Bus

MODBUS

0201

24V

PLC

+ +

BECKHOFF

PE PE

Power

Potential isolation

Additional characteristics of the Bus Terminal Controllers

Bus Terminal Controllers (BC) differ from Bus Couplers (BK) in that, in addition to K-Bus processing, a real-time PLC task is also running. Unlike Bus Couplers, the signals from the terminals are processed by the PLC task, while the fieldbus carries the in- and outputs of the PLC task. It is possible, however, to subdivide the Bus Terminals to that some Bus Terminals are pre-processed by the PLC task, while others are sent directly over the fieldbus to a supervising system.

Bus Terminal Controllers for various fieldbus systems

Various Bus Terminal Controllers can be used to couple the electronic terminal strip with integrated PLC task quickly and easily to different fieldbus systems. It is also possible to convert to another fieldbus system at a later time. The Bus Terminal Controller performs all the monitoring and control tasks that are necessary for operation of the connected Bus Terminals. The operation and configuration of the Bus Terminals is carried out exclusively by the Bus Terminal Controller. Fieldbus, K-Bus and I/O level are galvanically isolated.

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Power LEDs

Bus Coupler / power contacts

PLC

Basic Principles

If data exchange over the fieldbus fails, the PLC task continues to run as an autonomous system.

The interfaces

A Bus Terminal Controller has six different methods of connection. These interfaces are designed as plug connectors and as spring-loaded terminals.

The MODBUS – Bus Terminal Controller BC7300

MODBUS

24V

K-Bus Bus Coupler power supply 24 V DC / GND

Configuration and programming interface

8 7

BECKHOFF

BC 7300

PE PE

Power contacts feeding points

Power contacts

24 V DC to the topmost terminals “24 V” and “0 V”

Electrical power supply

The Bus Terminal Controllers require a 24 V DC supply for their operation. The connection is made by means of the upper spring-loaded terminals labelled “24 V” and “0 V”. This supply voltage feeds not only the Bus Coupler electronics via the K-Bus, but also the Bus Terminals. The power supply for the Bus Coupler electronics and that of the K-Bus are electrically separated from the potential of the field level.

Lower 3 terminal pairs for power feed

Maximum 24 V

Maximum 10 A

Power contacts feeding points

The bottom six connections with spring-loaded terminals can be used to feed the supply for the peripherals. The spring-loaded terminals are joined in pairs to a power contact. The feed for the power contacts has no connection to the voltage supply for the Bus Coupler. The design of the feed permits voltages of up to 24 V. The assignment in pairs and the electrical connection between feed terminal contacts allows the connection wires to be looped through to various terminal points. The current drawn from the power contact must not exceed 10 A for long periods. The current rating between two spring-loaded terminals is identical to that of the connecting wires.

Spring contacts on the side

Power contacts

On the right hand face of the Bus Terminal Controller there are three spring contacts for the power contact connections. The spring contacts are hidden in slots so that they can not be accidentally touched. By attaching a Bus Terminal the blade contacts on the left hand side of the Bus Terminal are connected to the spring contacts. The tongue and groove guides on the top and bottom of the Bus Terminal Controllers and of the Bus Terminals guarantees that the power contacts mate securely.

9 pin sub-D socket strip

Fieldbus connection

There is a recessed front face on the left hand side. The MODBUS connection plug can be inserted here. A full description of the fieldbus interfaces is found elsewhere in this manual. (In the section on The Medium: Plugs and Cables)

BC7300 9

Basic Principles

Serial interface under the front cover

6 contacts on the side

3 potential groups: Fieldbus K-Bus Peripheral level

Configuration and programming interface

The standard Bus Terminal Controllers have an RS232 interface at the bottom of the front face. The miniature connector can be joined to a PC with the aid of a connecting cable and either the KS2000 configuration software or TwinCAT BC. The interface allows the analog channels to be configured with the KS2000 software. The BC7300 is programmed via the same interface.

KS2000 Software

In order to link the MODBUS BK7300 Bus Terminal Controller and the KS2000 configuration software, the coupler's address selection switch must be set to "00", and it must be restarted (i.e. the coupler must be switched off and then on again). The MODBUS must not be connected.

TwinCAT BC

In order to link the MODBUS BK7300 Bus Terminal Controller and the TwinCAT BC programming software, the coupler's address selection switch must be set to "00", and it must be restarted (i.e. the coupler must be switched off and then on again). The MODBUS must not be connected.

K-Bus Contacts

In order to connect the Bus Coupler and Bus Terminals the Bus Coupler has gold contacts on the right hand side. When the Bus Terminals are pushed together the gold contacts automatically make the connection between the Bus Terminals. The voltage supply to the K-Bus electronics in the Bus Terminals and the data exchange between the Bus Coupler and the Bus Terminals is carried out by the K-Bus. A part of the data exchange takes place via a ring structure within the K-Bus. Opening the K-Bus, e.g. by pulling out one of the Bus Terminals, opens the ring. Data exchange is no longer possible. Special mechanisms nevertheless allow the Bus Coupler to identify the location of the interruption and to report it.

Electrical isolation

The Bus Terminal Controllers operate by means of three independent potential groups. The supply voltage feeds the K-Bus electronics in the Bus Terminal Controller and the K-Bus itself, which is electrically separate. The supply voltage is also used to generate the operating voltage for the fieldbus. Remark: All the Bus Terminals are galvanically isolated from the K-Bus. The K-Bus is thus galvanically isolated from everything else.

BC7300 10

Operating Modes of the Bus Terminal Controller

Start-up behaviour of the Bus Terminal Controller

Immediately after being switched on, the Bus Terminal Controller checks, in the course of a “self test”, all the functions of its components and the communication of the K-Bus. The red I/O LED blinks while this is happening. After completion of the self-test, the Bus Terminal Controller starts to test the attached Bus Terminals (in a "Bus Terminal test"), and reads in the configuration. An internal structure list is created from the Bus Terminal configuration. In case of an error, the Bus Terminal Controller enters the „STOP“ state. Once the start-up has completed without error, the Bus Terminal Controller enters the "fieldbus start" state.

Basic Principles

Power On self test

Bus Terminal test

Structure list

Error

PLC start /

Communication start

Mechanical structure

The system of the Beckhoff Bus Terminals is characterised by low physical volume and high modularity. When planning a project it must be assumed that at least one Bus Coupler and a number of Bus Terminals will be used. The mechanical dimensions of the Bus Couplers are independent of the fieldbus system. If large plugs are used, such as, for example, certain bus plugs for the Profibus, the maximum height of the housing can be exceeded.

Stop

BC7300 11

Basic Principles

020201

+++

PEPEPE

RUN

MODBUS

24V

Dimensions of a Bus Coupler in mm

4 9

PLC

F F

O H K C E B

0 0 3 7

C B

The total width in practical cases is composed of the width of the Bus Coupler with the bus end terminal and the width of the Bus Terminals in use. Depending on function, the Bus Terminals are 12 or 24 mm wide. The front wiring increases the total height of 68 mm by about 5 to 10 mm, depending on the wire thickness.

Assembly and connection

The Bus Coupler and all the Bus Terminals can be clipped by light pressure onto a 35 mm C-mounting rail. A locking mechanism prevents the individual housings from being pulled off again. For removal from the mounting rail the orange coloured tension strap releases the latching mechanism, allowing the housing to be pulled off the rail without any force. Work should only be carried out on the Bus Terminals and the Bus Coupler when switched off. Pulling out and inserting under power can cause undefined states to be temporarily caused. (A reset of the Bus Coupler, for example).

Maximum number of terminals

Up to 64 Bus Terminals can be attached to the Bus Coupler on the right hand side. When plugging the components together, be sure to assemble the housings with groove and tongue against each other. A properly working connection can not be made by pushing the housings together on the mounting rail. When correctly assembled, no significant gap can be seen between the attached housings.

The right hand part of the Bus Coupler can be compared to a Bus Terminal. Eight connections on the top permit connection with solid or fine wires. The connection is implemented with the aid of a spring device. The spring-loaded terminal is opened with a screwdriver or rod, by exerting gentle pressure in the opening above the terminal. The wire can be inserted into the terminal without any force. The terminal closes automatically when the pressure is released, holding the wire securely and permanently.

The connection between the bus coupler and the bus terminals is automatically realised by pushing the components together. The transfer of the data and the supply voltage for the intelligent electronics in the Bus Terminals is performed by the K-Bus. The supply of the field electronics is performed for the digital Bus Terminals through the power contacts.

BC7300 12

Plugging together the power contacts creates a supply rail. Note the circuit diagrams for the Bus Terminals, since some Bus Terminals do not loop these power contacts through, or only do so partially (e.g. analog Bus Terminals or 4 channel digital Bus Terminals). The potential feed terminals interrupt the power contacts, and represent the start of a new supply rail. The Bus Coupler can also be made use of to feed the power contacts.

Insulation testing

PE power contacts

The power contact labelled “PE” can be used as a protective earth. For safety reasons this contact mates first when plugging together, and can ground short-circuit currents of up to 125 A. Note that, for reasons of electromagnetic compatibility, the PE contacts are capacitatively coupled to the mounting rail. This can both lead to misleading results and to damaging the terminal during insulation testing. (e.g.: breakdown of the insulation from a 230 V power user to the PE conductor.) The PE conductor to the Bus Coupler must be disconnected for the insulation testing. In order to uncouple further feed locations for the purposes of testing, the feed terminals can be pulled at least 10 mm out from the connected group of other terminals. In that case, the PE conductors do not have to be disconnected.

The “PE” power contact must not be used for other potentials.

Basic Principles

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Basic Principles

Technical data

The MODBUS – the fieldbus-specific electrical data is listed in this section. The following table gives an overview of all the data:

Technical data BC7300

Supply voltage Input current

Power-on surge K Bus supply current up to Configuration facility Number of Bus Terminals Digital peripheral signals Analog peripheral signals Baud rate Protocol Bus connection

Voltage of the power contact

Power contacts current drawn

Electric strength

Typical weight Operating temperature Storage temperature Relative humidity Vibrations/Shock resistance EMC resistance burst / ESD Installation position Type of protection

PLC data

Programmability

Program size

Program memory

Data memory

Remanent flags

Runtime system

PLC cycle time

Programming languages

Station addresses

Baud rate in programming

mode

24 V DC 70mA +

(total K-Bus current)/4 500 mA max.

2.5 x steady operating current 1750 mA max. via KS2000 or the controller 64 256 inputs/outputs 128 inputs/outputs From 150 baud to 38400 baud RTU and ASCII D-Sub RS 485

9-pin 24 V DC / AC max.

10 A max.

500 Veff (power contact / supply voltage / fieldbus) none

170 g 0°C ... +55°C

-20°C ... +85°C 95% without dew formation conforms to IEC 68-2-6 / IEC 68-2-27 conforms to EN 50082 (ESD, Burst) / EN 50081 any IP20

via programming interface (TwinCAT BC/TwinCAT) approx. 3000 PLC statements 32 kbytes / 96 kbytes 32 kbytes / 64 kbytes 512 bytes 1 PLC task approx. 3 ms for 1000 instructions (including K-Bus I/O cycle) IL, LD, FBD, SFC, ST selectable to 99 via DIP switch

0 Programming mode and configuration mode 1 – 99 Slave address

19,200 baud, 8 data bits, even parity, one stop bit

Current consumption on the K-Bus

The Bus Terminals require energy for the operation of the K-Bus electronics, and this is supplied by the Bus Coupler. Find the current consumption of the K-Bus from the catalogue, or from the appropriate data sheets for the Bus Terminals. Consider the maximum output current of the Bus Coupler that is available for supply of the Bus Terminals. A special power supply terminal (KL9400) can be inserted at any location to insert more power into the K-Bus. Refer to Beckhoff’s technical support department regarding the use of a power supply terminal.

BC7300 14

Basic Principles

Digital signals (bit-oriented)

Analog signals (byte-oriented)

Special signals and interface

Default assignment of inputs/outputs to the process image

Peripheral Data in the Process Image

After being switched on, the Bus Coupler determines the configuration of the inserted input/output terminals. The assignment of the physical slots for the input/output channels and the addresses in the process image is carried out automatically by the Bus Coupler.

The Bus Coupler creates an internal assignment list, in which the input/output channels have a specific position in the process image. A distinction is made here according to inputs and outputs, and according to bit-oriented (digital) and byte-oriented (analog or complex) signal processing.

Two groups are created, one for inputs and the other for outputs. Each group has the byte-oriented channels in ascending sequence starting from the lowest address. The bit-oriented channels are placed after this block.

The digital signals are bit-oriented. This means that one bit in the process image is assigned to each channel. The Bus Coupler creates a memory area containing the current input bits, and ensures that the bits in a second memory area dedicated to the output channels are written out immediately.

The details of the assignment of the input and output channels to the controller's process image is explained fully with the aid of an example in the appendix.

The processing of all analog signals is always byte-oriented. Analog input and output values are represented in memory by two bytes each. Values are represented in SIGNED INTEGER or two‘s complement format. The number "0" stands for the input/output value "0 V", "0 mA" or "4 mA". The maximum value of an output or input value is represented, according to the standard settings, by "7FFF" (hex). Negative input or output values, e.g. 10 V, are represented from "8000" (hex). The intermediate values are correspondingly proportional. A range with a resolution of 15 bits is not achieved for all inputs and outputs. If the actual resolution is 12 bits, the last three bits have no effect in outputs, while as inputs they are read as "0". Each channel also has a control and status byte. The control and status byte is the lowest value byte. The master configuration software must specify whether the control/status byte is also mapped into the controller. An analog channel is represented in the process image by 2 bytes of user data.

A Bus Coupler supports Bus Terminals with other interfaces such as RS232, RS485, incremental encoder and others. These signals can be considered similarly to the analog signals named above. For some special signals the bit width of 16 is not sufficient. The Bus Coupler can support any byte width.

Once it has been switched on, the Bus Coupler finds out how many Bus Terminals are inserted, and creates an assignment list. The analog and digital channels, divided into inputs and outputs, are assembled into separate parts of this list. The assignment starts on the left next to the Bus Coupler. The software in the Bus Coupler collects the individual entries for each of the channels in order to create the assignment list counting from left to right.

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+ 33 hidden pages

BECKHOFF BC7300 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual