8.1 Agreement content

The inverter provides an RS485 communication interface and supports the Modbus-RTU communication protocol. Users can achieve centralized control through computers or PLCs using this communication protocol to set inverter operation commands, modify or read function code parameters, and read the inverter’s operating status and fault information.

This serial communication protocol defines the content and usage format of the information transmitted in serial communication. It includes the master polling (or broadcasting) format, the encoding method of the master, which includes the function code requesting action, transmission data, and error checking. The response from the slave also follows the same structure, including action confirmation, returning data, and error checking. If the slave encounters an error while receiving information or cannot complete the action requested by the master, it will organize a fault message as a response to the master.

8.1.1 Application Modes

The inverter connects to a “single master multiple slave” PC/PLC control network with an RS485 bus as a communication slave.

8.1.2 Bus Structure

1. Hardware Interface: Comes with communication interface A+ and B- terminal connectors.
2. Topology:
   • Single master multiple slave system. Each communication device in the network has a unique slave address, with one device serving as the communication master (PC host, PLC, HMI, etc.). The master initiates communication and performs parameter read or write operations on the slaves, while other devices act as communication slaves, responding to inquiries or communication operations from the master regarding themselves. Only one device can send data at a time, with the rest in a receiving state. The slave address is set within the range of 1 to 247, with 0 reserved for broadcast communication. Each slave address in the network must be unique.
3. Communication Transmission Mode:
   • Asynchronous serial, half-duplex transmission. Data in serial asynchronous communication is transmitted in the form of frames, with one frame sent at a time. According to the MODBUS-RTU protocol, when there is no data on the communication data line for a time greater than 3.5 byte transmission time, it indicates the start of a new communication frame.

     

     The built-in communication protocol of the inverter is the Modbus-RTU slave communication protocol, which can respond to the host’s “queries/commands” or perform corresponding actions based on the host’s “queries/commands,” and communicate data responses.

The host can be a personal computer (PC), industrial control equipment, or programmable logic controller (PLC), etc. The host can communicate individually with a specific slave or broadcast messages to all subordinate slaves. For individual access by the host through “queries/commands,” the accessed slave must return a response frame. For broadcast messages sent by the host, slaves do not need to provide responses.

8.1.3 Communication Data Structure

The Modbus protocol defines the format of communication data as shown below. The inverter only supports the reading or writing of Word-type parameters. The corresponding communication read operation command is 0x03, and the write operation command is 0x06. Byte or bit read/write operations are not supported:

In theory, the host computer can read several consecutive function codes at once (up to a maximum of 12), but it should be noted that it cannot skip the last function code in this group. Otherwise, an error response will be given.

If the slave detects a communication frame error or other reasons leading to unsuccessful read/write operations, it will respond with an error frame.

8.1.4 Frame Field Description

8.1.5 CMD Verification Method

The verification method is the CRC (Cyclical Redundancy Check) method, using the RTU frame format. The message includes an error detection field based on the CRC method. The CRC field checks the content of the entire message. The CRC field consists of two bytes containing a 16-bit binary value. It is calculated by the transmitting device and added to the message. The receiving device recalculates the CRC of the received message and compares it with the value in the received CRC field. If the two CRC values are not equal, it indicates a transmission error.

During the CRC calculation, the initial value is set to 0xFFFF, and then each consecutive 8-bit byte in the message is processed with the current value in the register. Only the 8-bit data in each character is valid for CRC, while the start bit, stop bit, and parity bit are invalid.

In the CRC generation process, each 8-bit character is individually XORed with the register content, and the result is shifted towards the least significant bit (LSB) direction, with the most significant bit (MSB) filled with 0. The LSB is extracted for checking. If the LSB is 1, the register is XORed with a preset value, and if the LSB is 0, no operation is performed. This process is repeated 8 times. After the last bit (8th bit) is completed, the next 8-bit byte is XORed individually with the current value in the register. The final value in the register is the CRC value after all bytes in the message have been processed. When adding CRC to the message, the low byte is added first, followed by the high byte. The CRC function is as follows:

unsigned int CRC16_CHK(unsigned char *data, unsigned char length)
{
  int j = 0;
  unsigned int crc Oxffff reg:
    while(length--)
    {
       crc reg *data++:
       for(j=0:j<8:j++)
          {
           if(reg crc 0x01)
             {
            reg_crc (reg_crc > 1) 0xa001:
             }
       else
             {
             reg_crc = reg_crc >> 1;
             }
          }
    }
    return reg_crc;
}

8.1.6 Function Code Parameter Addressing Rules:

For reading and writing function code parameters (some function codes cannot be changed and are only used by the manufacturer or for monitoring):

The parameter address is represented by the function code group number and label:

High byte: PO~PF (P group) AO-AF (A group) 70~7F (U group) Low byte: 00~FF

For example, if you want to access the range of function code P3-12, the access address for the function code is represented as F30CH.

Note:

• PF group: Parameters cannot be read or changed.
• U group: Parameters can only be read and cannot be changed.
• Some parameters cannot be changed when the inverter is in operation; some parameters cannot be changed regardless of the state of the inverter; when changing function code parameters, pay attention to the range, unit, and related instructions of the parameters.

Note:

1. Due to frequent EEPROM storage, it will reduce the service life of EEPROM. Therefore, for some function codes, no storage is required in communication mode, and only changing the value in RAM is sufficient.
2. If it is a P group parameter, to implement this function, simply change the high byte F of the function code address to 0. If it is an A group parameter, to implement this function, simply change the high byte A of the function code address to 4.

Writing to RAM corresponding function code addresses:

High byte: 00~0F (P group) 40~4F (A group) Low byte: 00~FF

For example, the function code P3-12 is not stored in EEPROM, the address is represented as 030CH; Function code A0-05 is not stored in EEPROM, the address is represented as 4005H.

Note: This address representation can only be used for writing to RAM, not for reading actions. When reading, it is an invalid address. For all parameters, you can also use command code 07H to implement this function.

8.1.7 Shutdown/Running Parameters Section:

Note:

1. The communication setting value is a percentage of the relative value, where 10000 corresponds to 100.00%, and -10000 corresponds to -100.00%.
2. For dimensional data of frequency, this percentage is relative to the maximum frequency (P0-10); for torque dimensional data, this percentage is P2-10, A2-48, A3-48, A4-48 (torque limit digital setting, corresponding to the first, second, third, and fourth motors respectively).

Control Commands Input to the Inverter: (Write Only)

Reading Inverter Status: (Read Only)

Parameter Lock Password Verification: (Returns 888H if the password check passes)

8.1.8 Output Control Commands

8.1.9 Inverter Fault Descriptions

8.1.10 PD Group Communication Parameter Description

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