Xylem H-3521 - Manual (Page 36)

5-6 SDI-12 Command and Response Protocol
H-3521
5.4 Continuous Measurements
This is a new command for the Version 1.2 SDI-12 Specification. Sensors that are able to
continuously monitor the phenomena to be measured, such as a cable position, do not require a
start measurement command. They can be read directly with the R commands (R0!...R9!). The R
commands work exactly like the D (D0!...D9!) commands. The only difference is that the R
commands do not need to be preceded with an M command.
The H-3521 does not support the aR0! continuous measurement commands because the
measurement and math operations require several seconds to complete..
5.5 Send Acknowledge Command
The Send Acknowledge Command returns a simple status response which includes the address of
the sensor. Any measurement data in the sensor's buffer is not disturbed.
Command Response
"a!" "a"
Where: a Is the sensor address ("0-9", "A-Z", "a-z", "*", "?").
Example of H-3521 "a!" command:
Command Response Time Values Description
"a!" "a" 0 sec 0 Return the address of sensor