Campbell Scientific TDRSDK Software Developement Kit - Manual (Page 6)

TDRSDK Software Development Kit for TDR100
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2. TDRSDK Description
2.1 Description of TDRCOM.DLL
TDRCOM.DLL is a dynamically linked library, DLL, comprised of functions
that allow control and monitoring of a TDR100 using PC serial
communications. The DLL functions are called by a program written by the
user, and the TDR100 communication protocol is transparent. Each DLL
function is defined with a name and a number. The functions perform a range
of TDR100 tasks including setting measurement parameters and collecting
waveform data.
2.2 Task complete or data available notification after command
issued
To enhance PC performance, query methods are used to determine if
information is available from the TDR100. Many of the TDRCOM.DLL API
functions only initiate commands to the TDR100 and do not continue to
execute while the TDR100 is running the assigned task. The Call-back and
State Machine methods are used to determine when the TDR100 has completed
a task.
2.2.1 Using the Call-back method
When programming in C++ or Pascal, a call-back procedure can be used to
notify the user program that data is available from the TDR100. The call-back
procedure uses 2 two parameters, (1) DLL command number and (2) error
code, to determine which command to execute and which part of the user
program to notify when data is available from TDR100. DLL function
RegCallBack is used to pass the address of the procedure in the user program
that will be notified when data available.
2.2.2 Using the State Machine method
The State Machine method is used in Visual Basic (including Excel). The
main part of the DLL will be implemented as a state machine, incrementally
stepping through short blocks of functionality (states). At regular time
intervals an Application Program Interface (API) function queries the state
machine to determine if data is available from the TDR100. When the data is
signaled to be available, a separate command is issued to retrieve the data from
the DLL to the user program
3. TDR100 Command Set
The TDR100 command set is also called the TDR100COM Application
Program Interface (API). Each command has an associated command number
that is used in DLL execution.