Xylem H-3311 - Manual (Page 14)

12
SDI-12 COMMAND &
RESPONSE PROTOCOL
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.
n is a single digit integer (0-9) 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.
Upon completion of the measurement, a service request “a” is sent to the data recorder
indicating the sensor data is ready. The data recorder may wake the sensor with a break and collect
the data anytime after the service request is received or the specified processing time has elapsed.
example of an ‘am!’ Command:
Command Response Time Values Description
‘aM!’ “a0012” 1 sec 2 Return encoder position
Subsequent Command Response
“aD0” a+X.XX+NNNN
Where:
X.XX = Current position (stage), in user programmable units
NNNN = Current position, in raw position counts
This “Measure” command causes a measurement sequence to be performed with a CRC appended
to the data. Data values generated in response to this command are stored in the sensor’s buffer
for subsequent collection using “D” commands. The data will be retained in the sensor until
another “M”, “C” or “V” command is executed.
Command Response Description
“aMC!” “atttn” Initiate measurement
Where:
a is the sensor address (“0-9”, “A-Z”, “a-z”, “*”, “?”).
M 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.
n is a single digit integer (0-9) 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
Upon completion of the measurement, a service request “a” is sent to the data recorder
indicating the sensor data is ready. The data recorder may wake the sensor with a break and
collect the data anytime after the service request is received or the specified processing time has
elapsed.
Measure Command with CRC