Xylem H-3311 - Manual (Page 16)

14
SDI-12 COMMAND &
RESPONSE PROTOCOL
The “Send Data” command returns sensor data generated as the result of previous “aM!”, “aC!” or
“aV!” commands. Values returned will be sent in 33 characters or less. The sensor’s data buffer will
not be altered by this command.
Command Response
“aD0!” through “aD9!” “apd.d ... pd.d”
Where:
a is the sensor address (“0-9”, “A-Z”, “a-z”, “*”, “?”).
D0..D9 are upper-case ASCII characters.
p Is a polarity sign (+ or -)
d.d represents numeric digits before and/or after the decimal. A decimal may be
used in any position in the value after the polarity sign. If a decimal is not used,
it will be assumed to be after the last digit.
For example: +3.29 +23.5 -25.45 +300
If one or more values were specified and a “aD0!” returns no data (a only), it means that
the measurement was aborted and a new “M” command must be sent. The following is an example
of the “aD0!” command.
Send Data Command
example of an "aD0!" command:
Previous command Response
"aM!" "a0012"
Subsequent Command Response
"aD0" +X.XX+NNNN
Where:
X.XX = Current position (stage), in user programmable units
NNNN = Current position (raw counts), in raw position counts
Where:
a is the sensor address (“0-9”, “A-Z”, “a-z”, “*”, “?”).
C is an upper-case ASCII character
ttt is a three digit integer (000-999) specifying the maximum time, in seconds, the sensor
will take to complete the command and have measurement data available in its buffer.
nn is a two digit integer (00-99) specifying the number of values that will be placed in the
data buffer. If “n” is zero (0), no data will be available using subsequent “D” commands.
The data recorder may wake the sensor with a break and collect the data anytime after the
specified processing time has elapsed.