文档介绍：MODBUS Application Protocol Specification
Content 1 Introduction.............................................................................. 3
Scope of this document..............................................................3
References.................................................................................3
2 Abbreviations ........................................................................... 4
3 Context .................................................................................... 4
4 General description.................................................................. 5
Protocol description....................................................................5
Data Encoding............................................................................7
MODBUS data model.................................................................7
MODBUS Addressing model......................................................9
Define MODBUS Transaction.....................................................9
5 Function Code Categories..................................................... 11
Public Function Code Definition ...............................................12
6 Function codes descripitons .................................................. 12
01 (0x01) Read Coils................................................................12
02 (0x02) Read Discrete Inputs................................................14
03 (0x03) Read Holding Registers ...........................................16
04 (0x04) Read Input Registers ...............................................17
05 (0x05) Write Single Coil ......................................................19
06 (0x06) Write Single Register ...............................................20
07 (0x07) Read Exception Status (Serial Line only).................21
08 (0x08) Diagnosti