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Measurement Sequence
Reading multiple input registers is supported, but only one type (moisture or temperature) can
be read at a time. Reading multiple registers should also only request the number of soil mois-
ture or temperature sensor measurements that are supported by the probe. Attempting to read
more values than are supported will return an exception code value of 02 indicating illegal data
address.
A new measurement is triggered by a read request to the input registers (either read single or
read multiple). The first read command will initiate the start of a measurement (soil moisture or
soil temperature) and will respond to the master with an ACKNOWLEDGE (05) exception re-
sponse. Moisture measurements take approximately 200 ms per segment. Temperature meas-
urements take approximately 200 ms per sensor. The master should wait for this amount of
time to expire before attempting to retrieve the measurement values with another read com-
mand. This command will return the measured values. It does
not
trigger another measure-
ment until another read input command is received.
Attempts to read the registers before the measurement time has elapsed will be ignored; there
will be no response, the sensor will only respond once the measurements are completed.
Holding Registers (Read: Function Code 03, Write: Function Code 06)
These are registers that can be read and written. These registers contain scaling and polyno-
mial coefficients, as well as operational settings (communication settings, sensor address, etc.)
Read response timeout is typically immediate. Write response timeout is delayed by the non-
volatile write time of the registers and is approximately 50 ms maximum per register written [to
be verified].
When reading and writing to these registers the offset address used is one less than the lower
portion of the register address, for example register 40001 is at 16 bit offset 0, register 40002
is at 16-bit offset 1.
The GPLP probes support holding registers 40001-40204. Note: some registers are only appro-
priate for probes with those segments. For example, GPLP-3 does not support registers associ-
ated with segment 4 and up.
Register
Description
Default Value
40001-40002
Segment 1 scale factor (32-bit IEEE float)*
0.09765625*
40003-40004
Segment 1 third order polynomial A (32-bit IEEE float)
0
40005-40006
Segment 1 third order polynomial B (32-bit IEEE float)
0
40007-40008
Segment 1 third order polynomial C (32-bit IEEE float)
1
40009-40010
Segment 1 third order polynomial D (32-bit IEEE float)
0
40011-40012
Segment 2 scale factor (32-bit IEEE float)*
0.09765625*
40013-40014
Segment 2 third order polynomial A (32-bit IEEE float)
0
40015-40016
Segment 2 third order polynomial B (32-bit IEEE float)
0
40017-40018
Segment 2 third order polynomial C (32-bit IEEE float)
1
40019-40020
Segment 2 third order polynomial D (32-bit IEEE float)
0
