MODBUS Application Protocol Specification

1 Introduction .. 2

1.1 Scope of this document . 2

1.2 References.. 2

2 Abbreviations .. 3

3 Context 3

4 General description .. 5

4.1 Protocol description. 5

4.2 Data Encoding 7

4.3 MODBUS data model . 7

4.4 Define MODBUS Transaction . 9

5 Function Code Categories .. 11

5.1 Public Function Code Definition 12

6 Function codes descripitons 12

6.1 01 (0x01) Read Coils.12

6.2 02 (0x02) Read Discrete Inputs.14

6.3 03 (0x03) Read Holding Registers ..17

6.4 04 (0x04) Read Input Registers 18

6.5 05 (0x05) Write Single Coil.20

6.6 06 (0x06) Write Single Register 22

6.7 15 (0x0F) Write Multiple Coils25

6.8 16 (0x10) Write Multiple registers 28

6.9 20 (0x14) Read File Record 29

6.10 22 (0x16) Mask Write Register .34

6.11 23 (0x17) Read/Write Multiple registers35

6.12 43 (0x2B) Read Device Identification.38

7 MODBUS Exception Responses.. 43