User Manual EM303B General Purpose Inverter 13 Modbus Communication Protocol 13.1 Application Scope Applicable series: EM303B Applicable network: Support Modbus protocol, RTU format, with single-master/multi-slave Communication network of RS485 bus. The typical RTU message frame format: 13.2 Physical Interface RS485 asynchronous half-duplex Communication mode. Default data format of communication terminal ofkeypad: 1-8-N-1rbits rate: 9600bps. Default data format of RS485 terminal: 1-8-N-1ofe.
rmat, with sing Data format 1-8-N-1, 1-8-O-1, 1-8-E-1, optional bits rates 4800bps, 9600bps, 19200bps, and 38400bps Shielded twisted-pair cable is recommended Communication cable to lower external interference. 13.3 Protocol Format ADU Initial Block of Stop Block of Frame ≥ Idle Periods of 4 Bits Frame ≥ Idle Periods of 4 Bits Figure 12-1 Protocol Format The parity in ADU (Application Data Unit) is obtained via the CRC16 parity of the 1 st three parts of ADU and switching the low bytes and high bytes. Low bytes of CRC parity go first, and high bytes of it follow in the protocol format. 13.4 Explanation of Command Command code 0x03:Read parameter and status of inverter.
177 Start Bit Device Address Function Code Data CRC Stop Bit T1-T2-T3-T4 8Bit 8Bit n*8Bit 16Bit T1-T2-T3-T4 Address of Command Slave Code Address of Slave Command Code U Data CRC Parity Data CRC Parity ADU Item Byte No. Range Master requests: Address of slave 1 0～127 Command Code 1 0x03 Register start address 2 0x0000～0xFFFF Register number 2 0x0000～0x0008