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OUT OF YOUR HANDS

A PC Interface for Hand-Held Devices
by Kock Kin Ko

Start • Creating GUI and Menu • PC Interface Software • CVI Windows Programming Basics • Working Together • Plotting Performance Graphs • How Serial Com Operates • Big Endian Data Becomes Little • Sources 

CVI WINDOWS PROGRAMMING BASICS

Based on the GUI main panel in file car05.uir, the main program framework is automatically generated and saved into car05.c. Listing 1 shows the main program framework. You can see the C main function main() and the menu callback functions of the File menu (i.e., Save(), Open(), Analysis(), Print_panel(), and Exit()).

To maintain program modularity, Com menu callback functions SetUp(), ReqData(), and Closecom() are moved to another file, com05.c. Note that what automatically generated were the frame structures of these menu callback functions. CVI does provide codes for main() and Exit() (the former starts the Windows program by executing RunUserInterface() and the latter quits the program by executing QuitUserInterface(0)).

Before proceeding further, it’s necessary to introduce some of the basic CVI functions (shown in Listing 2). GetCtrlVal() gets the data content of the textbox and loads that data into a buffer szBuffer. panelMain indicates that the textbox is an object on the main panel. The SetCtrlAttribute() sets the LED color to red. The LED has a constant ID: COMON. This LED has a label name Com Link SetUp, not shown in the function.

It’s not absolutely necessary to memorize the case-sensitive function names, the Constant IDs, or the parameters. You can just call up their function panels from the user interface library and click to select Constant IDs TEXTBOX or COMON, or click to select attribute parameter ATTR_OFF_COLOR and its value VAL_RED.

You do need to define a system variable szBuffer to hold the textbox data. A more complicated function is FileSelectPopUp(), which enables users to look for a directory and create a file. In its function panel, just click on "SAVE button" and option "allow user change directory." Next, key in file type "*.car" and the title message of the file dialogue panel "Enter name of file to save" and then declare a system variable szFileName to hold file name and its directory.

As an example of how to fill up a callback function, consider saving a file using the File menu callback function Save(). First, FileSelectPopUp() enables you to create a file. Next, the file is opened for "write" by pFile(). Then GetCtrlVal() copies the content of the textbox into a buffer. Finally, fwrite() writes the buffer data into the file and fclose() closes the file.

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