Holding Registers
Appendix B
: Modbus Protocol
Airnet® II 4-Channel Particle Sensors Operations Manual
B-5
Holding Registers
For Airnet II, any change to the Holding registers creates a new configuration and so
stops the unit if sampling. The new configuration, when completely defined, will be
run on the next start-up.
The real-time clock is set via a "time_t" value.
The sample interval and Hold/Tare times are single registers for number of seconds to
process. This should make it easy for the host to set.
Coils
Table B-3
Holding registers
Holding Registers
Description (Setup)
Comment
40001
ushort
Real Time Clock (high)
time_t
40002
ushort
Real Time Clock (low)
time_t
40003
ushort
Sample Interval
Seconds
40004
ushort
Hold/Tare Time
Seconds
40005
ushort
Repeat Count
Repeat Count
1
The data collection coil will enable/disable sampling. It will start a sequence of samples if the
repeat count has been set.
Read & Write: 1 = Sampling Enabled, 0 = Sampling Disabled
2
The data available coil is used to both inform the host that data is now available and to delete
the next queued data packet (if desired).
Read: 1 = Data Available, 0 = No Data Available
Write: 0 = Delete queued data element
3
The data clear coil will delete all data in the queue.
Write: 1 = Delete all queued data
4
The reset sensor coil will reset the sensor.
Write: 1 = Reset Sensor
5 & 6
The Green and Red LED (usually a single dual-color LED) can be set/read independently.
Read & Write: 1 = LED on, 0 = LED off
7
The external alarm does not exist on the Airnet II
8
The IEEE float control will change the appropriate registers (refer to the map) from a dual-
register integer with fixed scaling to a dual-register IEEE-754 Float representation. This value
can also be set into non-volatile storage via the setup interface (“set instrument float n” –
where n=1 on or n=0 off).
Read & Write: 1 = Float mode enabled, 0 = Float mode disabled
9 – 32
Spare.
