Function Code 3: Read Holding Registers Request 1 Byte 1 to 255 PLC Node Address 1 Byte 0x03 Function Code 2 Bytes 0x0000 to 0xFFFF Starting Address 2 Bytes 1 to 125 Quantity of Registers Response 1 Byte 1 to 255 PLC Node Address 1 Byte 0x03 Function Code 1 Byte 2 * N (Quantity of registers) Byte Count N * 2 Bytes Value(s) Holding Registers Function Code 4: Read Input Registers Request 1 Byte 1 to 255 PLC Node Address 1 Byte 0x04 Function Code 2 Bytes 0x0000 to 0xFFFF Starting Address 2 Bytes 1 to 125 Quantity of Registers Response 1 Byte 1 to 255 PLC Node Address 1 Byte 0x04 Function Code 1 Byte 2 * N (Quantity of registers) Byte Count N * 2 Bytes Value(s) Holding Registers
Function Code 3: Read Holding Registers Request PLC Node Address 1 Byte 1 to 255 Function Code 1 Byte 0x03 Starting Address 2 Bytes 0x0000 to 0xFFFF Quantity of Registers 2 Bytes 1 to 125 Response PLC Node Address 1 Byte 1 to 255 Function Code 1 Byte 0x03 Byte Count 1 Byte 2 * N (Quantity of registers) Holding Registers N * 2 Bytes Value(s) Function Code 4: Read Input Registers Request PLC Node Address 1 Byte 1 to 255 Function Code 1 Byte 0x04 Starting Address 2 Bytes 0x0000 to 0xFFFF Quantity of Registers 2 Bytes 1 to 125 Response PLC Node Address 1 Byte 1 to 255 Function Code 1 Byte 0x04 Byte Count 1 Byte 2 * N (Quantity of registers) Holding Registers N * 2 Bytes Value(s)
PI_ModbusE_4.0.2.80.docx