ActiveX control brings bit manipulation to Windows
Steve Hageman, Agilent Technologies, Santa Rosa, Ca -- EDN, May 25, 2000
Nothing compares with the C language for working with bits. C provides a rich set of signed and unsigned number formats, along with many intrinsic bit-manipulation operators. However, most of the popular rapid-application-development Windows languages lack C's ability to easily work with bits. Visual Basic is such a language. Although it's hard to find a faster language to develop a small to midsized application in Windows, Visual Basic starts to show its weakness when it comes time to talk to hardware. Hardware programming is usually bit-oriented. That is, it's necessary to turn bits on and off or shift out serial streams to get the hardware to operate correctly. The ActiveX control serves just these types of bit-manipulation needs (Figure 1). The control includes functions for changing binary strings to numbers, a hex-output function, the ability to set and clear bits in a word, and the ever-needed shift-left and -right functions. As an example, many of the three-wire serial devices need to have a setup word shifted to them. Suppose you need to shift the setup word 0111 1101 first to an A/D converter to initiate a conversion on some channel. You can use the functions in the ActiveX control to easily effect the shift operation, as follows:
In the above example, val has the values 1, 0, 1, 1, 1, 1, 1, 0 during each iteration of the loop. The routine can then clock these bits to the A/D converter as required by the hardware. If the operation requires MSB first, you can use the ShiftLeft function. The SetBit and ClearBit functions are useful when using a port as clock and data lines, because you can set individual bits as needed instead of doing entire port writes. Any modern programming language that can use ActiveX controls, such as Agilent VEE, Visual Basic, Delphi, and others, can use the functions given here. Click here to download the ActiveX control. The routine includes all the functions listed in Figure 1, plus a few more, with application examples. (DI #2534)
