Xylem H-335 - Manual (Page 17)

Chapter 2
SDI-12 Command and Response Protocol
H-335
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-335 sensor. Included is a description of the commands and data format
supported by the H-335.
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-335 SDI-
12 sensor. The H-335 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.