Airnet II Particle Sensor Operations Manual
Page B-1
Appendix B
Modbus Protocol
Communications with the Airnet II can be done via Modbus TCP. The following Modbus
register map has comments and notes to help with its intended use.
Modbus Overview
The map contains three sections:
The supported functions include:
•
Any registers accessed but not defined will generate an address error.
•
Spare coils/registers will “set” without error and always return a zero value.
•
Registers set with invalid data will return a function error.
There is a setting available that toggles the interpretation of selected dual-register
values. These values can be interpreted as integer representations of floating point
numbers with a fixed scaling factor or as IEEE-754 floating point representations of that
value. Refer to the register map to determine which register pairs have this feature
applied. This setting can be made in the setup interface, and saved in non-volatile
storage, or set real-time via a coil.
1
Input registers
– Read only information for ID and data collection
2
Holding registers – Read/Write parameters for configuring the device
3
Coils
– Read/write individual bits to control the device
1
Read Coils
5
Write Single Coil
15
Write Multiple Coils
4
Read Input Registers
3
Read Holding Registers
6
Write Single Holding Register
16
Write Multiple Holding Registers
23
Read/Write Multiple Holding Registers
22
Mask Write Holding Register