A very basic example of writing C code for the 8051

Code:

Code (Text):

1. /*************************************************************************
2. * basic.c - The basics of writing C code for the 8051 using the Keil
3. *  development environment.  In this case, a simple program will be
4. *  constructed to make a binary counter on Port 0.
5. */
6.  
7. /*
8. * As always with C, the included header files should come first.  Most
9. * every project for the 8051 will want to include the file reg51.h.  This
10. * header file contains the mapping of registers to names, such as setting
11. * P0 (port 0) to address 0x80.  This allows the coder to use the keyword
12. * "P0" in their code whenever they wish to access Port 0.  For the complete
13. * list of registers named, view the file.
14. */
15.  
16. #include
17.  
18. /*
19. * Other header files may be included after reg51.h, including any headers
20. * created by the user.
21. */
22.  
23. /*
24. * The C program starts with function main().  In the case of a program
25. * written using multiple .c files, main can only occur in one of them.
26. * Unlike in programming user applications for a standard computer, the
27. * main() function in a Keil program for the 8051 takes no inputs and
28. * returns no output, thus the declaration has implied void types.
29. */
30.  
31. /*************************************************************************
32. * main - Program entry point
33. *
34. * INPUT: N/A
35. * RETURNS: N/A
36. */
37.  
38. main()
39. {
40.     unsigned int i;        /* will be used for a delay loop */
41.  
42.     /* First, Port 0 will be initialized to zero */
43.  
44.     P0 = 0;
45.  
46.     /*
47.       * Now the counter loop begins.  Because this program is intended
48.       * to run in an embedded system with no user interaction, and will
49.       * run forever, the rest of the program is placed in a non-exiting
50.       * while() loop.
51.       */
52.  
53.     while (1==1)
54.     {
55.           /*
56.                   * This is a very unpredictable method of implementing a delay
57.                   * loop, but remains the simplest.  More reliable techniques
58.                   * can be done using the using the built-in timers.  In this
59.                   * example, though, the for() loop below will run through 60000
60.                   * iterations before continuing on to the next instruction.
61.                   * The amount of time required for this loop varies with the
62.                   * clock frequency and compiler used.
63.                   */
64.  
65.           for (i = 0; i < 60000; i++) {;}
66.  
67.         /* Increment Port 0 */
68.  
69.         P0 = P0 + 1;
70.     }
71.  
72. }