Page B-6
Airnet II Particle Sensor Operations Manual
Appendix B
Modbus Protocol
Data Packet Processing
The unit can provide real-time data or queued data or both. There is only one section
of Input registers assigned for data to handle this information.
If the unit is setup to queue data then the data shown is the oldest data in the queue.
The data available coil bit will be set if there is data in the queue. The data available bit
can be cleared in which case that data element shown is popped-off of the queue. If
there is more data in the queue, the new data will be shown and the data available coil
bit will be set. If there is no more data in the queue, the data available bit will only be
set again once the next sample is completed.
If the queue is set to one, then the data shown is always the last data processed and is
representative of real-time data only. Since the queue is circular - the next sample will
replace the single one in the queue.
Queued data will always be available - even when not sampling.
If there is no data available - the input registers will yield zeros. This is done instead of
generating an execution exception so that the customer can simply read the data
packet, along with the Device Status, in one command.
Table B-4
Coils
Coils
Description (Coils)
Comment
00/01
Data Collection
On/Off
Sampling Control
00/02
Data Available
Yes/No
Data Available/Queue Control
00/03
Data Clear
Toggle
Data Queue Delete
00/04
Reset Sensor
Toggle
Reset control
00/05
Status LED: Green
On/Off
Status LED: Green Control
00/06
Status LED: Red
On/Off
Status LED: Red Control
00/07
External Alarm
On/Off
External alarm
n/a
00/08
IEEE-754 Float
On/Off
Modbus Float representation
Spare
24 spare coils
Reserve "common" coils
00/33
Set Digital Output 1
On/Off
option 2
00/34
Set Digital Output 2
On/Off
option 2
00/35
Set Digital Output 3
On/Off
option 2
00/36
Set Digital Output 4
On/Off
option 2
00/37
Set Digital Output 5
On/Off
option 2
