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TABLE OF CONTENTS
1.0 INTRODUCTION....................................................................................................................1
2.0 ADVANTAGES OF SDI-12 ....................................................................................................1
3.0 SDI-12 ELECTRICAL INTERFACE....................................................................................2
3.1 Serial Data Line .............................................................................................................3
3.1.1 Voltage Transitions .........................................................................................3
3.1.2 Impedance .......................................................................................................3
3.2 Ground Line ...................................................................................................................4
3.2.1 Transient Protection ........................................................................................4
3.3 12-Volt Line ...................................................................................................................5
3.4 Connectors .....................................................................................................................5
4.0 SDI-12 COMMUNICATIONS PROTOCOL ........................................................................5
4.1 Baud Rate and Byte Frame Format ................................................................................6
4.2 Allowable Characters .....................................................................................................6
4.3 Device Addresses ...........................................................................................................7
4.4 SDI-12 Commands and Responses ................................................................................7
4.4.1 Acknowledge Active Command (a!) ..............................................................9
4.4.1.1 Examples of the Acknowledge Active Command (a!) ...................9
4.4.2 Send Identification Command (aI!) ................................................................9
4.4.2.1 Example of the Send Identification Command ............................10
4.4.3 Address Query Command (?!) ......................................................................10
4.4.4 Change Address Command (aAb!) ...............................................................11
4.4.5 Start Measurement Command (aM!) ............................................................11
4.4.5.1 Aborting a Measurement ..............................................................12
4.4.6 Service Request .............................................................................................13
