Руководство по эксплуатации MCD2 - Modbus RTU (EN)

MCD2 series communication protocol Modbus RTU

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MCD2 series communication protocol Modbus RTU 1. Preface This communication protocol manual mainly describes the networking mode of the soft starter and the related aspects of the communication protocol, which is convenient for users to realize the configuration. This soft starter can provide the user with RS485/RS232 communication interface. The interface of the host computer equipment (such as PC, PLC, DCS controller, etc.) to communicate, realize the centralized monitoring and remote operation of the soft start (such as setting various parameters, control start, stop, read various parameters and soft start working status, etc.).

This communication protocol is an interface specification document designed to realize the above func- tions, please read carefully and follow the programming to realize remote and network control of the soft starter. 2. Networking method 3. Modbus RTU Overview General knowledge For the exchange of information between automation systems, between automation systems and con- nected decentralized field devices, serial fieldbuses are today mainly used as communication systems. Thousands of applications have strongly demonstrated that up to 40% of the costs of wiring, commission- ing and maintenance can be saved by using fieldbus technology.

All relevant information of field devices, such as input and output data, parameters, diagnostic data, can be transmitted using only two wires. Fieldbuses used in the past tended to be manufacturer‐specific fieldbuses and line is not compatible. The fieldbuses in use today are almost completely open and stand- ardized. This means that users can choose the best product at the most reasonable price without relying on each individual manufacturer. Modbus RTU is an international, open field bus standard. As an easy‐to‐implement fieldbus protocol, Modbus has been successfully applied all over the world.

Application areas include automation in produc- tion processes, process control and building automation. Basic Features Modbus RTU determines the technical and functional characteristics of a serial field bus system that connects distributed digital automation equipment together. It is designed to deliver data at extremely high speeds at the field level.

The central control equipment here, such as PLC or PC, communicates the 2 Classified as Business Host as PL or Host as PLC RS232 232/485 conversion module RS485 Soft starter Soft starter Soft starter Host as PL or Host as PLC RS232 232/485 conversion RS485 module RS485 Soft starter Soft starter Single master multi-slave network diagram Single master single slave network diagram

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MCD2 series communication protocol Modbus RTU input and output data of switch quantity and/or analog quantity with the peripheral field station through the relevant high‐speed serial interface. Master device ‐ controls data exchange on the bus. The master is allowed to send information without an external request. Slave Devices ‐ Peripherals such as AKS series soft starters. They do not have the abil- ity to access the bus, so that is, they can only acknowledge messages that have been received, or, at the request of the master, send messages to the master. Slaves are also often referred to as passive stations. The following rules generally apply:

• On a bus, only one master station is allowed to work (single master bus system). • Up to 247 slave stations can be connected to a bus. • The communication is always initiated by the master station, and the slave station can only respond to the request of the master station. • Protection features: “sum check” and parity bits. • There are two ways for the communication between the master station and the field device (slave station): • Individual communication method ‐ direct request to a specific field device. (Slave address cannot be “0”): • “Normal” operation: The master sends a request to a field device, which then responds. • Broadcast mode ‐ the total request for all field devices.

(Slave address is “0”): The master sends a request (telegram) to all bus stations. For example, sending an “urgent” command without any slave response. 4. Protocol Basic Structure • message structure Based on serial data transmission, it is transmitted bit by bit. RS485 interface: asynchronous, half‐dual. The default data format is 8‐N‐1, 19200bps. • Interface method As shown in the figure below, pin 15 is the B(‐) line, and pin 16 is the A(+) line. Classified as Business 3

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MCD2 series communication protocol Modbus RTU The RS485 communication interface is placed in a high‐impedance state in addition to sending data in general. In order to prevent the output from being unstable and causing malfunction at this time, the RS485 communication interface circuit of the computer sometimes has a built‐in safety circuit that boosts and attenuates the output signal to maintain a low‐impedance state. Please install a terminating resistor when communicating. As shown in Figure 3: RS485 interface circuit receive circuit transmit circuit Attenuation resistor Lifting resistor Terminating resistor Figure 3. Install terminating resistor. Note:

Please do not operate the function codes related to communication during the communication process. During the communication process, the normality of the communication cannot be guaranteed, which will lead to the unstable operation of the soft starter. For the function code settings related to computer and serial communication, please refer to Table 2: Table 2 Serial communication function code setting table • Protocol format Modbus ADU (Application Data Unit) consists of address, function code, actual data and CRC. Modbus PDU (Protocol Data Unit) consists of two parts:

function code and actual data ADU frame start interval ≥ 3.5 characters Slave address ADR Functin code CMD DATA checksum ORC frame end interval ≥ 3.5 characters PDU The Modbus ADU (Application Data Unit) check is obtained by exchanging the high and low bytes of the CRC16 checksum of the first three parts of the ADU. If the operation request fails, the PDU (Protocol Data Unit) response is an error code and an abnormal code.

4 Classified as Business Function code Setting value Illustrations F1.00 control mode 2, 4, 5, 6 The communication controller is valid, oth- erwise only data can be read F8.00 Communication enabled 1 When set to 1, the communication is valid F8.01 local address 1~247 Local address, 0 is the broadcast address

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