beautypg.com
8.
Appendix—Modbus Additional Information .........................................................................55
8.1
Modbus Tutorial ...................................................................................................55
8.2
Modbus Modes ....................................................................................................55
8.3
Protocol Overview ................................................................................................56
8.4
General Message Formats ...................................................................................56
8.5
RTU Message Format ..........................................................................................56
8.5.1
Computer (Master) Message Format ................................................................56
8.5.2
Device (Slave) Response Format .....................................................................57
8.6
ASCII Message Format ........................................................................................57
8.6.1
Computer (Master) Message Format ................................................................57
8.6.2
8.7
IP Message Format..............................................................................................58
8.7.1
Computer (Master) Message Format ................................................................58
8.7.2
Device (Slave) Message Format ......................................................................58
8.8
Data Addresses (Registers) .................................................................................58
8.9
Function Codes ....................................................................................................59
8.10
Standard Message Formats .................................................................................59
8.10.1
Read Holding Registers ................................................................................60
8.10.2
Write Holding Register ..................................................................................60
8.10.3
Write Holding Registers ................................................................................60
8.10.4
Mask Write Register......................................................................................61
8.10.5
Report Slave ID ............................................................................................62
8.11
Instrument Manufacturer Data Types ...................................................................63
8.11.1
Short .............................................................................................................63
8.11.2
Unsigned Short .............................................................................................63
8.11.3
Long .............................................................................................................63
8.11.4
Unsigned Long..............................................................................................64
8.11.5
Float .............................................................................................................64
8.11.6
Double ..........................................................................................................64
8.11.7
Character ......................................................................................................64
8.11.8
String ............................................................................................................64
8.11.9
Time .............................................................................................................65
8.12
Exception Codes ..................................................................................................66
8.13
Extended Exception Codes ..................................................................................67
8.14
Probe Register Map Layout .................................................................................68
4
