MODBUS/TCP 是一种用于工业自动化设备间通信的协议，它基于 TCP/IP 协议，提供了连接导向性和数据编码规范。该规范详细介绍了不同功能代码，如读取/写入多个寄存器、读取/写入输入和输出状态等，并分为不同的符合性类别。MODBUS/TCP 使用 'big-endian' 数据编码，允许通过参考号码访问不同表格中的数据。协议结构中，请求和响应都包含交易标识符、协议标识符和长度字段，且MODBUS的CRC校验在MODBUS/TCP中不再使用，依赖于TCP/IP的校验机制。
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OPEN Modbus /TCP SPECIFICATION
Release 1.0, 29 March 1999
Andy Swales
Schneider Electric
aswales@modicon.com
Contents
Contents............ 2
1. Status of this specification...... 3
2. Overview........ 3
2.1 Connection-oriented.............. 3
2.2 Data encoding........ 4
2.3 Interpretation of reference numbers......... 4
2.4 Implied length philosophy.... 5
3. Conformance class summary... 5
3.1 Class 0...... 5
3.2 Class 1...... 5
3.3 Class 2...... 6
3.4 Machine/vendor/network specific functions....... 7
4. Protocol structure............. 7
5. Protocol reference by conformance class.................... 8
5.1 Class 0 commands detail............... 9
5.1.1 Read multiple registers (FC 3)................ 9
5.1.2 Write multiple registers (FC 16).............. 9
5.2 Class 1 commands detail............. 10
5.2.1 Read coils (FC 1).................. 10
5.2.2 Read input discretes (FC 2).............. 10
5.2.3 Read input registers (FC 4).............. 11
5.2.4 Write coil (FC 5) 11
5.2.5 Write single register (FC 6).................. 12
5.2.6 Read exception status (FC 7).................. 12
5.3 Class 2 commands detail............. 13
5.3.1 Force multiple coils (FC 15)..... 13
5.3.2 Read general reference (FC 20)..... 14
5.3.3 Write general reference (FC 21)..... 15
5.3.4 Mask write register (FC 22)..... 16
5.3.5 Read/write registers (FC 23)............ 16
5.3.6 Read FIFO queue (FC 24)..... 17
6. Exception codes................ 17
Appendices..... 19
A. Client and Server Implementation Guidance.......... 19
A.1 Client design.......... 19
A.2 Server design.......... 20
A.2.1 Multithreaded server... 20
A.2.2 Single-threaded server 21
A.3 Required and expected performance 22
B. Data Encoding for non-word data........................... 23
B.1 Bit numbers within a word...................... 23
B.2 Multi-word quantities..... 24
B.2.1 984 Data Types.................. 24
B.2.2 IEC-1131 data types 25
1. Status of this specification
Initial release 3 Sept 1997
Draft for public review.
Re-release 29 March 1999 at Revision 1.0.
No technical changes, clarifications only.
Added Appendices A and B in response to common implementation questions.
This specification of Modbus/TCP is being published by being publicly visible on the World Wide Web. It is intended for the benefit of developers wishing to use MODBUS/TCP as an interoperability standard in the field of industrial automation.
Since MODBUS and MODBUS/TCP are in reality ‘de-facto’ standards, in that many vendors and products implement it already, this specification primarily explains the specific encoding of MODBUS messages over the TCP communication protocol universally available on the Internet.
2. Overview
MODBUS/TCP is a variant of the MODBUS family of simple, vendor-neutral communication protocols intended for supervision and control of automation equipment. Specifically, it covers the use of MODBUS messaging in an ‘Intranet’ or ‘Internet’ environment using the TCP/IP protocols. The most common use of the protocols at this time are for Ethernet attachment of PLC’s, I/O modules, and ‘gateways’ to other simple field buses or I/O networks.
The MODBUS/TCP protocol is being published as a (‘de-facto’) automation standard. Since MODBUS is already widely known, there should be little information in this document which could not be obtained elsewhere. However, an attempt has been made to clarify which functions within MODBUS have value for interoperability of general automation equipment, and which parts are ‘baggage’ from the alternate use of MODBUS as a programming protocol for PLC’s.
This is done below by grouping supported message types into ‘conformance classes’ which differentiate between those messages which are universally implemented and those which are optional, particularly those specific to devices such as PLC’s.
2.1 Connection-oriented
In MODBUS, data transactions are traditionally stateless, making them highly resistant to disruption from noise and yet requiring minimal
OPEN Modbus /TCP SPECIFICATION
Release 1.0, 29 March 1999
Andy Swales
Schneider Electric
aswales@modicon.com
Contents
Contents............ 2
1. Status of this specification...... 3
2. Overview........ 3
2.1 Connection-oriented.............. 3
2.2 Data encoding........ 4
2.3 Interpretation of reference numbers......... 4
2.4 Implied length philosophy.... 5
3. Conformance class summary... 5
3.1 Class 0...... 5
3.2 Class 1...... 5
3.3 Class 2...... 6
3.4 Machine/vendor/network specific functions....... 7
4. Protocol structure............. 7
5. Protocol reference by conformance class.................... 8
5.1 Class 0 commands detail............... 9
5.1.1 Read multiple registers (FC 3)................ 9
5.1.2 Write multiple registers (FC 16).............. 9
5.2 Class 1 commands detail............. 10
5.2.1 Read coils (FC 1).................. 10
5.2.2 Read input discretes (FC 2).............. 10
5.2.3 Read input registers (FC 4).............. 11
5.2.4 Write coil (FC 5) 11
5.2.5 Write single register (FC 6).................. 12
5.2.6 Read exception status (FC 7).................. 12
5.3 Class 2 commands detail............. 13
5.3.1 Force multiple coils (FC 15)..... 13
5.3.2 Read general reference (FC 20)..... 14
5.3.3 Write general reference (FC 21)..... 15
5.3.4 Mask write register (FC 22)..... 16
5.3.5 Read/write registers (FC 23)............ 16
5.3.6 Read FIFO queue (FC 24)..... 17
6. Exception codes................ 17
Appendices..... 19
A. Client and Server Implementation Guidance.......... 19
A.1 Client design.......... 19
A.2 Server design.......... 20
A.2.1 Multithreaded server... 20
A.2.2 Single-threaded server 21
A.3 Required and expected performance 22
B. Data Encoding for non-word data........................... 23
B.1 Bit numbers within a word...................... 23
B.2 Multi-word quantities..... 24
B.2.1 984 Data Types.................. 24
B.2.2 IEC-1131 data types 25
1. Status of this specification
Initial release 3 Sept 1997
Draft for public review.
Re-release 29 March 1999 at Revision 1.0.
No technical changes, clarifications only.
Added Appendices A and B in response to common implementation questions.
This specification of Modbus/TCP is being published by being publicly visible on the World Wide Web. It is intended for the benefit of developers wishing to use MODBUS/TCP as an interoperability standard in the field of industrial automation.
Since MODBUS and MODBUS/TCP are in reality ‘de-facto’ standards, in that many vendors and products implement it already, this specification primarily explains the specific encoding of MODBUS messages over the TCP communication protocol universally available on the Internet.
2. Overview
MODBUS/TCP is a variant of the MODBUS family of simple, vendor-neutral communication protocols intended for supervision and control of automation equipment. Specifically, it covers the use of MODBUS messaging in an ‘Intranet’ or ‘Internet’ environment using the TCP/IP protocols. The most common use of the protocols at this time are for Ethernet attachment of PLC’s, I/O modules, and ‘gateways’ to other simple field buses or I/O networks.
The MODBUS/TCP protocol is being published as a (‘de-facto’) automation standard. Since MODBUS is already widely known, there should be little information in this document which could not be obtained elsewhere. However, an attempt has been made to clarify which functions within MODBUS have value for interoperability of general automation equipment, and which parts are ‘baggage’ from the alternate use of MODBUS as a programming protocol for PLC’s.
This is done below by grouping supported message types into ‘conformance classes’ which differentiate between those messages which are universally implemented and those which are optional, particularly those specific to devices such as PLC’s.
2.1 Connection-oriented
In MODBUS, data transactions are traditionally stateless, making them highly resistant to disruption from noise and yet requiring minimal
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