C-1
Appendix C. SDI-12 Sensor Support
C.1 Introduction
SDI-12, Serial Data Interface at 1200 baud, is a protocol developed to simplify
sensor and data logger compatibility. Only three wires are necessary — serial
data, ground, and 12 V. With unique addresses, multiple SDI-12 sensors can
connect to a single SDI-12 terminal on a Campbell Scientific data logger.
This appendix discusses the structure of SDI-12 commands and the process of
querying SDI-12 sensors. For more detailed information, refer to version 1.4 of
the SDI-12 protocol, available at
For additional information, refer to the
SDI-12 Sensors | Transparent Mode
SDI-12 Sensors | Watch or Sniffer Mode
videos.
C.2 SDI-12 Command Basics
SDI-12 commands have three components:
Sensor address (a)
– a single character and the first character of the command.
Use the default address of zero (0) unless multiple sensors are connected to the
same terminal.
Command body
– an upper case letter (the “command”), optionally followed by
one or more alphanumeric qualifiers.
Command termination (!)
– an exclamation mark.
An active sensor responds to each command. Responses have several standard
forms and always terminate with <CR><LF> (carriage return and line feed).
Standard SDI-12 commands are listed in TABLE
TABLE C-1. Campbell Scientific Sensor SDI-12 Command and
Response Set
Name
Command
Response
1
Acknowledge
Active
a!
a<CR><LF>
Send Identification
aI!
allccccccccmmmmmmvvvxxx...xx
<CR><LF>
Start Verification
aV!
atttn <CR><LF>
Address Query
?!
a<CR><LF>
Change Address
aAb!
b<CR><LF>
Start Measurement
aM!
aM1!
...
aM9!
atttn<CR><LF>
