Xylem H-340SDI - Manual (Page 15)

Chapter 2
SDI-12 Command and Response Protocol
H-340SDI
SDI-12 Command and Response Protocol 2-1
2.1 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-340SDI sensor. Included is a description of the commands
and data format supported by the H-340SDI.
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-340SDI sensor. The H-340SDI 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.