User Manual of EM730 Series Inverter Fig. 12- 20 Schematic Diagram of Message Frame in RTU Mode The RTU message includes the address code, PDU (Protocol Data Unit) and CRC [3] check. The PDU includes the function code and data part (mainly including the register address, number of registers, register content and the like; the detailed definitions of function codes are different, as shown in 11.3.3Function code ). [3]: the low byte of CRC check is in front of the high byte. 11.3.2 Address code 11.3.3 Function code The classification of MODBUS function codes is shown in Fig. 12-21. Fig. 12- 21 Classification of MODBUS Function Codes 369 Address Range Purpose 1 - 247 Slave 0 Broadcast