UniData Communication Systems Starlog Prologger 7001, User Manual

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Appendix D - USING THE SDI-12 INTERFACE
D - 1 INTRODUCTION
SDI-12 is an industry-originated, serial digital interface bus designed to allow
connection of a wide variety of transducers (meteorological, hydrological,
water quality, etc.) to a single SDI-12 data recorder with a single cable bus.
The PROLOGGER is such a data recorder. This means that you can, for
instance, connect several SDI-12 sensors to a PROLOGGER and not have to
worry about combinations of signal types (RS-232, parallel analog, BCD,
serial analog, RS-422, etc.).
A unique feature of the PROLOGGER is its ability to operate as an SDI-12
Data Recorder or an SDI-12 Sensor.
This appendix assumes that the reader is familiar with the operation of the
SDI-12 Sensor (the Sensor) and the PROLOGGER (the Recorder). For more
information see the STARLOG Programmer’s Manual, number 6201.
D - 2 THEORY OF OPERATION
When the PROLOGGER sends a “break signal”, the Sensor awakes and
captures the SDI-12 command following the break signal. If the command is
valid, the Sensor reads its address setting to see whether or not its address is
in fact being called, or if the address of some other device (at another
location) is being sought. If the logger is looking for a different address, the
Sensor will go back to sleep until another break signal is received.
If the address being sent belongs to the Sensor, it will scan the instructions
coming from the logger to see what action is required. The two most
important commands at this time are:
Measure: If the Sensor receives the START MEASUREMENT
command, it will report back to the logger the number of
parameters enabled for measurement, and that these parameters
are available to be sent to the logger immediately.
Data: If the Sensor receives the SEND DATA command, it will send
the last parameter readings measured to the PROLOGGER for
storage.
PROLOGGER Hardware
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