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Most advanced programming environments provide an interface to DLL’s. However,

all have peculiarities which must be understood for successful use. For example, in the VB

environment an argument passed to the API is considered a pointer to a data type unless it is

noted to be passed ‘ByVal’. The VB type ‘String’ is a pointer, so the argument would be a

pointer to a pointer unless the ByVal qualifier was applied to make it a pointer to a character

array. The definitions of the API functions as required by VB can be found in the source code

for the TR122 top level application.

The exported function list contains several classes of functions. These include abstract

functions which contain identifiable hardware and user features of a transient recorder – such as

setting a sample rate or issuing a trigger. Another set of functions deals with calibration of the

instrument, for use in operations covered in section 4 of this manual. Finally, a set of functions

performs operations on an internal device independent bitmap (DIB) which forms the basis of the

oscilloscope display screen.

In addition to exported items and others enumerated in the header file, the source code

contains a number of private functions and data variables. For the most part the private data are

unique to a particular process. A process is an instance of the top level application, such as the

user application for the TR122 instrument in a particular CPCI slot. For example, each instance

of the top level application will have its own screen DIB and its own settings. If data are to be

shared between processes, the API must take advantage of operating system resources for that

purposes. For example, each process must be aware of which TR122 instruments are already

in use by another process. In addition, a number of operating system semaphores and message

flags are used to communicate between processes and internal threads.

Even most advanced users will use this source code as a reference to build additional

higher level applications. It would be unusual to actually modify this source code. However,

the source code can be a valuable reference in understanding how each of the functions behave.

There is extensive documentation in the source code itself. This manual will provide a roadmap

of exported functions, an overview of their intended use, and how they fit in to the overall

software design.

DDC TR122 User Manual

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