Xylem H-312-22 - Manual (Page 21)

Chapter 4
SDI-12 Command and Response Protocol
H-312
SDI-12 Command and Response Protocol 4-1
4.0 SDI-12 Command and Response Protocol
This is a brief description of the Serial Digital Interface (SDI-12) Command and Response
Protocol used by the W
ATER LOG ® Series Model H-312 sensor. Included is a description of the
commands and data format supported by the H-312.
Refer to the document "A SERIAL DIGITAL INTERFACE STANDARD FOR HYDROLOGIC
AND ENVIRONMENTAL SENSORS.” Version 1.2 April 12, 1996 Coordinated by the SDI-12
Support Group, 135 East Center, Logan, Utah.
During normal communication, the data recorder sends an address together with a command to
the H-312 SDI-12 sensor. The H-312 then replies with a "response." In the following
descriptions, SDI-12 commands and responses are enclosed in quotes. The SDI-12 address and
the command/response terminators are defined as follows:
" a " Is the sensor address. The following ASCII Characters are valid addresses:
"0-9", "A-Z", "a-z", "*", "?". Sensors will be initially programmed at the
factory with the address of "0" for use in single sensor systems. Addresses
"1 to 9" and "A to Z" or "a to z" can be used for additional sensors
connected to the same SDI-12 bus. Address "*" and "?" are "wild card"
addresses which select any sensor, regardless of its actual address.
" ! " Is the last character of a command block.
" " Are carriage return (0D) hex and line feed (0A) hex characters. They are
the last two characters of a response block.
Notes:
• All commands/responses are upper-case printable ASCII characters.
• Commands must be terminated with a "!" character.
• Responses are terminated with characters.
• The command string must be transmitted in a contiguous block with no gaps of more
than 1.66 milliseconds between characters.