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Modbus RTU
Operating guide
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Danfoss Modbus RTU Operating guide

MAKING MODERN LIVING POSSIBLE
Operating Instructions
Modbus RTU
Contents Modbus RTU Operating Instruction
Contents
1 Safety and Conformity
1.1 Safety Precautions
1.1.1 Safety Precautions - Continued 3
1.4 CE Labelling
1.4.1 CE Conformity and Labelling 5
1.5.2 Aggressive Environments 6
2 Introduction
2.1 Introduction
3 3
5
8 8
3 RS-485 Installation and Set-up
4 Modbus RTU Message Framing Structure
4.1.2 Timing Constraints 12
4.1.3 Modbus RTU Message Structure 13
4.1.5 Address Field 13
4.1.8 CRC Check Field 13
4.1.9 Coil and Register Addressing 14
9
12
4.1.13 Parameter Handling 16
4.1.14 Storage of Data 16
MG92B102 - VLT® is a registered Danfoss trademark 1
Contents Modbus RTU Operating Instruction
5 How to Control the Frequency Converter
5.1 How to Control the Frequency Converter
5.2 Parameter for Modbus RTU
5.2.2 Access via PCD write/read 18
6 Function Code Examples
6.1 Examples
6.1.2 Force/Write Single Coil (05 HEX) 21
7 FC Control Profile
18 18 18
21 21
24
8 Parameters
8.1 Parameters: 8-** Communications and Options
8.1.3 8-3* FC Port Settings 30
8.1.4 8-4* FC MC protocol set 31
9 Troubleshooting
9.1.1 Modbus Exception Codes 35
9.1.3 8-81 Bus Error Count 35
9.1.4 8-82 Slave Messages Rcvd 35
9.1.5 8-83 Slave Error 36
Index
28 28
35
37
2 MG92B102 - VLT® is a registered Danfoss trademark
Safety and Conformity Modbus RTU Operating Instruction
1 Safety and Conformity
1.1 Safety Precautions
WARNING
The voltage of the frequency converter is dangerous whenever connected to mains. Incorrect installation of the motor, frequency converter or fieldbus may cause death, serious personal injury or damage to the equipment. Consequently, the instructions in this manual, as well as national and local rules and safety regulations, must be complied with.
Safety Regulations
1. The mains supply to the frequency converter must be disconnected whenever repair work is to be carried out. Check that the mains supply has been disconnected and that the necessary time has elapsed before removing motor and mains supply plugs.
2. The [Off] button on the control panel of the frequency converter does not disconnect the mains supply and consequently it must not be used as a safety switch.
3. The equipment must be properly earthed, the user must be protected against supply voltage and the motor must be protected against overload in accordance with applicable national and local regulations.
4. The earth leakage current exceeds 3.5 mA.
5. Protection against motor overload is not included in the factory setting. If this function is desired, set 1-90 Motor Thermal Protection to data value ETR trip 1 [4] or data value ETR warning 1 [3].
6. Do not remove the plugs for the motor and mains supply while the frequency converter is connected to mains. Check that the mains supply has been disconnected and that the necessary time has elapsed before removing motor and mains plugs.
7. Note that the frequency converter has more voltage sources than L1, L2 and L3, when load sharing (linking of DC intermediate circuit) or external 24 V DC are installed. Check that all voltage sources have been disconnected and that the necessary time has elapsed before commencing repair work.
1.1.1
Safety Precautions - Continued
Warning against unintended start
1. The motor can be brought to a stop with digital commands, bus commands, references or a local stop, while the frequency converter is connected to mains. If personal safety considerations (e.g. risk of personal injury caused by contact with moving machine parts following an unintentional start) make it necessary to ensure that no unintended start occurs, these stop functions are not sufficient. In such cases the mains supply must be disconnected or the Safe Stop function must be activated.
2. The motor may start while setting the parameters. If this means that personal safety may be compromised (e.g. personal injury caused by contact with moving machine parts), motor starting must be prevented, for instance by use of the Safe Stop function or secure disconnection of the motor connection.
3. A motor that has been stopped with the mains supply connected, may start if faults occur in the electronics of the frequency converter, through temporary overload or if a fault in the power supply grid or motor connection is remedied. If unintended start must be prevented for personal safety reasons (e.g. risk of injury caused by contact with moving machine parts), the normal stop functions of the frequency converter are not sufficient. In such cases the mains supply must be disconnected or the Safe Stop function must be activated.
NOTE
When using the Safe Stop function, always follow the instructions in the section Safe Stop of the Design Guide.
4. Control signals from, or internally within, the frequency converter may in rare cases be activated in error, be delayed or fail to occur entirely. When used in situations where safety is critical, e.g. when controlling the electromagnetic brake function of a hoist application, these control signals must not be relied on exclusively.
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Safety and Conformity Modbus RTU Operating Instruction
11
WARNING
1.2.1 Caution
High Voltage
Touching the electrical parts may be fatal - even after the equipment has been disconnected from mains. Also make sure that other voltage inputs have been disconnected, such as external 24 V DC, load sharing (linkage of DC intermediate circuit), as well as the motor connection for kinetic back up. Systems where frequency converters are installed must, if necessary, be equipped with additional monitoring and protective devices according to the valid safety regulations, e.g law on mechanical tools, regulations for the prevention of accidents etc. Modifications on the frequency converters by means of the operating software are allowed.
CAUTION
The DC link capacitors remain charged after power has been disconnected. Be aware that there may be high voltage on the DC link even when the Control Card LEDs are turned off. A red LED is mounted on a circuit board inside the frequency converter to indicate the DC bus voltage. The red LED will stay lit until the DC link is 50 V DC or lower. To avoid electrical shock hazard, disconnect the frequency converter from mains before carrying out maintenance. When using a PM-motor, make sure it is disconnected. Before doing service on the frequency converter wait at least the amount of time indicated below:
NOTE
Hazardous situations shall be identified by the machine builder/integrator who is responsible for taking necessary preventive means into consideration. Additional monitoring and protective devices may be included, always according to valid national safety regulations, e.g. law on mechanical tools, regulations for the prevention of accidents.
NOTE
Crane, Lifts and Hoists: The controlling of external brakes must always have a redundant system. The frequency converter can in no circumstances be the primary safety circuit. Comply with relevant standards, e.g. Hoists and cranes: IEC 60204-32 Lifts: EN 81
Protection Mode Once a hardware limit on motor current or DC link voltage is exceeded the frequency converter will enter “Protection mode”. “Protection mode” means a change of the PWM modulation strategy and a low switching frequency to minimize losses. This continues 10 s after the last fault and increases the reliability and the robustness of the frequency converter while re-establishing full control of the motor. In hoist applications “Protection mode” is not usable because the frequency converter will usually not be able to leave this mode again and therefore it will extend the time before activating the brake – which is not recommendable. The “Protection mode” can be disabled by setting 14-26 Trip Delay at Inverter Fault to zero which means that the frequency converter will trip immediately if one of the hardware limits is exceeded.
Voltage [V] Power [kW] Waiting Time [min] 380-500 0.25-7.5 4 11-75 15 90-200 20 250-800 40 525-690 11-75 (frame
size B and C)
37-315 (frame
size D)
355-1000 30
15
20
1.2.2 Protection Mode
Equipment containing electrical components may not be disposed of together with domestic waste. It must be separately collected with electrical and electronic waste according to local and currently valid legislation.
1.3.1 Software Version
Design Guide
Software version: 6.4x
This Design Guide can be used for all frequency converters with software version 6.4x. The software version number can be seen from 15-43 Software Version.
NOTE
It is recommended to disable protection mode in hoisting applications (14-26 Trip Delay at Inverter Fault = 0)
4 MG92B102 - VLT® is a registered Danfoss trademark
Safety and Conformity Modbus RTU Operating Instruction
1.4 CE Labelling
1.4.1 CE Conformity and Labelling
The machinery directive (2006/42/EC) Frequency converters do not fall under the machinery directive. However, if a frequency converter is supplied for use in a machine, Danfoss provide information on safety aspects relating to the frequency converter. What is CE Conformity and Labelling? The purpose of CE labelling is to avoid technical trade obstacles within EFTA and the EU. The EU has introduced the CE label as a simple way of showing whether a product complies with the relevant EU directives. The CE label says nothing about the specifications or quality of the product. Frequency converters are regulated by two EU directives: The low-voltage directive (2006/95/EC) Frequency converters must be CE labelled in accordance with the low-voltage directive of January 1, 1997. The directive applies to all electrical equipment and appliances used in the 50 - 1000 V AC and the 75 - 1500 V DC voltage ranges. Danfoss CE-labels in accordance with the directive and issues a declaration of conformity upon request. The EMC directive (2004/108/EC) EMC is short for electromagnetic compatibility. The presence of electromagnetic compatibility means that the mutual interference between different components/ appliances does not affect the way the appliances work. The EMC directive came into effect January 1, 1996. Danfoss CE-labels in accordance with the directive and issues a declaration of conformity upon request. To carry out EMC-correct installation, see the instructions in this Design Guide. In addition, Danfoss specify which standards our products comply with. Danfoss offer the filters presented in the specifications and provide other types of assistance to ensure the optimum EMC result.
The frequency converter is most often used by profes­sionals of the trade as a complex component forming part of a larger appliance, system or installation. The EMC directive (2004/108/EC)
What Is Covered
1.4.2
The EU "Guidelines on the Application of Council Directive 2004/108/EC" outline three typical situations of using a frequency converter. See below for EMC coverage and CE labelling.
1. The frequency converter is sold directly to the end-consumer. The frequency converter is for example sold to a DIY market. The end-consumer is a layman. Installing the frequency converter for
use with a hobby machine, a kitchen appliance, etc. For such applications, the frequency converter must be CE labelled in accordance with the EMC directive.
2. The frequency converter is sold for installation in a plant. The plant is built up by professionals of the trade. It could be a production plant or a heating/ventilation plant designed and installed by professionals of the trade. Neither the frequency converter nor the finished plant has to be CE labelled under the EMC directive. However, the unit must comply with the basic EMC requirements of the directive. This is ensured by using components, appliances, and systems that are CE labelled under the EMC directive.
3. The frequency converter is sold as part of a complete system. The system is being marketed as complete and could e.g. be an air-conditioning system. The complete system must be CE labelled in accordance with the EMC directive. The manufacturer can ensure CE labelling under the EMC directive either by using CE labelled components or by testing the EMC of the system. If only CE labelled components are used, it is unneccessary to test the entire system.
Danfoss Frequency Converter and CE
1.4.3 Labelling
CE labelling is a positive feature when used for its original purpose, i.e. to facilitate trade within the EU and EFTA.
However, CE labelling may cover many different specifi­cations. Check what a given CE label specifically covers.
The covered specifications can be very different and a CE label may therefore give the installer a false feeling of security when using a frequency converter as a component in a system or an appliance.
Danfoss CE labels the frequency converters in accordance with the low-voltage directive. This means that if the frequency converter is installed correctly, we guarantee compliance with the low-voltage directive. Danfoss issues a declaration of conformity that confirms our CE labelling in accordance with the low-voltage directive.
The CE label also applies to the EMC directive provided that the instructions for EMC-correct installation and filtering are followed. On this basis, a declaration of conformity in accordance with the EMC directive is issued.
The Design Guide offers detailed instructions for instal­lation to ensure EMC-correct installation. Furthermore,
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Safety and Conformity Modbus RTU Operating Instruction
11
Danfoss specifies which our different products comply with.
Danfoss provides other types of assistance that can help to obtain the best EMC result.
1.4.4 Compliance with EMC Directive 2004/108/ECEMC Directive
IP54/55. As an extra protection, coated printed circuit boards can be ordered as an option.
Airborne Particles such as dust may cause mechanical, electrical, or thermal failure in the frequency converter. A typical indicator of excessive levels of airborne particles is dust particles around the frequency converter fan. In very dusty environments, use equipment with enclosure rating IP54/55 or a cabinet for IP00/IP20/TYPE 1 equipment.
2004/108/EC
In environments with high temperatures and humidity,
As mentioned, the frequency converter is mostly used by professionals of the trade as a complex component forming part of a larger appliance, system, or installation. Note that the responsibility for the final EMC properties of the appliance, system or installation rests with the installer. As an aid to the installer, Danfoss has prepared EMC instal­lation guidelines for the Power Drive system. The standards and test levels stated for Power Drive systems are complied with, provided that the EMC-correct instructions for installation are followed, see the section EMC Immunity in the Design Guide.
Air Humidity
1.5.1
The frequency converter has been designed to meet the IEC/EN 60068-2-3 standard, EN 50178 pkt. 9.4.2.2 at 50° C.
corrosive gases such as sulphur, nitrogen, and chlorine compounds cause chemical processes on the frequency converter components.
Such chemical reactions rapidly affect and damage the electronic components. In such environments, mount the equipment in a cabinet with fresh air ventilation, keeping aggressive gases away from the frequency converter. An extra protection in such areas is a coating of the printed circuit boards, which can be ordered as an option.
NOTE
Mounting frequency converters in aggressive environments increases the risk of stoppages and considerably reduces the life of the converter.
Aggressive Environments
1.5.2
A frequency converter contains a large number of mechanical and electronic components. All are to some extent vulnerable to environmental effects.
CAUTION
The frequency converter should not be installed in environments with airborne liquids, particles, or gases capable of affecting and damaging the electronic components. Failure to take the necessary protective measures increases the risk of stoppages, thus reducing the life of the frequency converter.
Degree of protection as per IEC 60529 The Safe Stop function may only be installed and operated in a control cabinet with degree of protection IP54 or higher (or equivalent environment). This is required to avoid cross faults and short circuits between terminals, connectors, tracks and safety-related circuitry caused by foreign objects.
Liquids can be carried through the air and condense in the frequency converter and may cause corrosion of components and metal parts. Steam, oil, and salt water may cause corrosion of components and metal parts. In such environments, use equipment with enclosure rating
Before installing the frequency converter, check the ambient air for liquids, particles, and gases. This is done by observing existing installations in this environment. Typical indicators of harmful airborne liquids are water or oil on metal parts, or corrosion of metal parts.
Excessive dust particle levels are often found on instal­lation cabinets and existing electrical installations. One indicator of aggressive airborne gases is blackening of copper rails and cable ends on existing installations.
D and E enclosures have a stainless steel back-channel option to provide additional protection in aggressive environments. Proper ventilation is still required for the internal components of the frequency converter. Contact Danfoss for additional information.
1.5.3
Vibration and Shock
The frequency converter has been tested according to the procedure based on the shown standards:
The frequency converter complies with requirements that exist for units mounted on the walls and floors of production premises, as well as in panels bolted to walls or floors.
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Safety and Conformity Modbus RTU Operating Instruction
IEC/EN 60068-2-6: Vibration (sinusoidal) - 1970
•
IEC/EN 60068-2-64: Vibration, broad-band random
•
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Introduction Modbus RTU Operating Instruction
2 Introduction
22
confirming the action taken, any data to be returned, and
2.1 Introduction
This manual explains how to physically establish and configure communication between the Danfoss FC Series and a controller using the Modbus RTU protocol.
This instruction is intended to be used for both instruction and reference. It only briefly touches on the basics of the Modbus protocol whenever necessary to gain an understanding of the Modbus RTU. This instruction is also intended to serve as a guideline to specify and optimise the communication system. Even experienced Modbus programmers, should read these entire operating instructions before starting programming since important information can be found in all sections.
Modbus RTU Overview
2.1.1
Regardless of the type of physical communication networks, the Modbus RTU Overview describes the process a controller uses to request access to another device. This process includes how the Modbus RTU responds to requests from another device, and how errors are detected and reported. It also establishes a common format for the layout and contents of message fields. During communications over a Modbus RTU network, the protocol determines:
an error-checking field. If an error occurs in receipt of the message, or if the slave is unable to perform the requested action, the slave constructs an error message, and sends it in response, or a time-out occurs.
How each controller learns its device address Recognizes a message addressed to it Determines which actions to take Extracts any data or other information contained
in the message
If a reply is required, the controller constructs the reply message and sends it. Controllers communicate using a master-slave technique in which only one device (the master) can initiate transactions (called queries). The other devices (slaves) respond by supplying the requested data to the master, or by taking the action requested in the query. 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. No responses are returned to broadcast queries from the master. The Modbus RTU protocol establishes the format for the master’s query by placing into it the device (or broadcast) address, a function code defining the requested action, any data to be sent, and an error-checking field. The slave’s response message is also constructed using Modbus protocol. It contains fields
8 MG92B102 - VLT® is a registered Danfoss trademark
Wire # 1
Wire # 2
Data In Data Out
175ZB021.10
Wire #1
Wire #2
175ZB028.10
130BA060.11
68 69 68 69 68 69
RS 485
RS 232 USB
+
-
RS-485 Installation and Set... Modbus RTU Operating Instruction
3 RS-485 Installation and Set-up
3.1.1 Overview
The Modbus RTU protocol is based on the built-in RS-485 (EIA-485) interface on the FC Drive series control card. RS-485 is a two-wire bus-interface that allows multi-drop network topology i.e. nodes can be connected as a bus (daisy chain), or via drop cables from a common trunk line. Danfoss uses the two-wire system where the communi­cation between master and slave is half-duplex, i.e. it cannot transmit and receive at the same time.
Each signal uses one twisted-pair line — two wires twisted around themselves. This is known as balanced data transmission or differential voltage transmission (see Illustration 3.1). The signal on one wire is ideally the exact opposite of the signal on the second wire. In other words, if one wire is transmitting a high, the other wire transmits a low, and vice versa (see Illustration 3.2). Since RS-485 is a multipoint communication system, all devices are connected to the single twisted-pair cable.
3.1.2 Cable Specifications
When choosing a transmission line for RS-485, it is necessary to examine the required distance of the cable and the data rate of the system. Losses in a transmission line are a combination of AC losses (skin effect), DC conductor loss, leakage, and AC losses in the dielectric. In high-quality cable, the conductor losses and the dielectric losses are on the same order of magnitude.
The recommended maximum Modbus cable length between the frequency converter and the Controller must not exceed 30 m (100 feet). While the RS-485 specification does not specify cabling, the recommendation is 0.25 mm2/24 AWG shielded twisted-pair cable with a shunt capacitance of 16 pF/ft and 100 Ω impedance. Another choice is the same cable commonly used in the twisted­pair Ethernet cabling. This cable is commonly referred to as Category 5 cable. The cable has a maximum capacitance of 17 pF/ft (14.5 pF/ft typical) and characteristic impedance of 100 Ω.
Network Connection
3.1.3
3
3
Illustration 3.1 Balanced Data Transmission
Illustration 3.2 Differential Concept
The Modbus RTU uses master/slave architecture, where each slave device has its unique address and responds only to packets addressed to this device. The packets are generated by the master (Controller), which periodically polls all connected slave devices. Data travels over the single line in both directions.
According to the EIA-485 specification a total number of 32 nodes can be connected to one Modbus RTU network segment, and a total of 247 nodes in a network are supported. Network segments are divided with repeaters.
NOTE
Each repeater counts for a node in each segment it is installed. Every node connected to the same network must have a unique nodes address, across all segments.
One or more frequency converters can be connected to a control (or master) using the RS-485 standardized interface. Terminal 68 is connected to the P signal (TX+, RX+), while terminal 69 is connected to the N signal (TX-,RX-).
If more than one frequency converter is connected to a master, use parallel connections.
MG92B102 - VLT® is a registered Danfoss trademark 9
130BB021.10
12 13 18 19 27 29 32
33 20 37
Remove jumper to enable Safe Stop
61 68 69 39 42 50 53 54 55
130BT310.10
1
2
N O
V LT
BUS TER. OFF-ON
A53 A54 U- I U- I
3
RS-485 Installation and Set... Modbus RTU Operating Instruction
Illustration 3.3 Control Card Terminals
RS-485 Bus Termination
3.1.4
The RS-485 bus terminate by a resistor network at both ends only. For this purpose, set switch S801 on the control card for "On".
10 MG92B102 - VLT® is a registered Danfoss trademark
Fieldbus cable
Min.200mm
90° crossing
130BA080.11
RS-485 Installation and Set... Modbus RTU Operating Instruction
3.1.5 EMC Precautions
The following EMC precautions are recommended to achieve interference-free operation of the RS-485 network.
Relevant national and local regulations, for example regarding protective earth connection, must be observed. The RS-485 communication cable must be kept away from motor and brake resistor cables to avoid coupling of high frequency noise from one cable to another. Normally a distance of 200 mm (8 inches) is sufficient, but keeping the greatest possible distance between the cables is generally recommended, especially where cables run in parallel over long distances. When crossing is unavoidable, the RS-485 cable must cross motor and brake resistor cables at an angle of 90o.
3
3
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