Updating Chapter 2

17. January 2008 by pilot.

Continuing with the review of the code examples for the latest revision of the MPLAB C30 compiler (3.02) it is time to look at Chapter 2.

There is a single example used in this chapter and the code needs no massaging beside remembering to disable the advanced warnings or otherwise ignore the obvious complaint about main() type (see previous post).

Here is the code: Loop.c

Notice that the definition of DELAY can be shortened to just 16 to speed up considerably (1000 x) the simulation when using only MPLAB SIM and the Logic Analyzer window.

We can also take the opportunity to complete the exercises proposed at the end of the chapter:

1. The first exercise required us to replace the simple on/off sequence with a count.
   Declaring an 8-bit integer called count (this might require some of you to peek into chapter 4 already) we get the mission accomplished quickly: Exercise 2-1.
2. The second exercise required us to replace the on/off sequence with a rotating pattern. To make things more interesting we will choose a 16-bit variable that we will call pattern. The exercise is actually quite valuable because it forces us to recognize the fact that in C language there is no concept of rotation, but there are only shift operators. So unless we make use of inline assembly, we are forced to take things in our hands and perform a three steps sequence: Exercise 2-2. Commenting and un-commenting different sections you will see examples of right and left rotations.
   Adding all PORTA pins to the channels of the Logic Analizer will help get the full picture:
   

The C programming experts among you will not fail to recognize the opportunity to use special “shortcuts” using advanced operators such as +=, >>=, <<= and some conditional expressions trickery.

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