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Text File  |  1979-12-31  |  689b  |  24 lines
  1. /* --------------------------------- pc8254.h ------------------------------- */
  2.  
  3. /* This is part of the flight simulator 'fly8'.
  4.  * Author: Eyal Lebedinsky (eyal@ise.canberra.edu.au).
  5. */
  6.  
  7. /* Definitions for the timer chip 8254. Used for timekeeping and speaker
  8.  * control.
  9. */
  10.  
  11. #define CHANNEL_0    0x0040        /* system tick */
  12. #define    CHANNEL_2    0x0042        /* speaker tone */
  13. #define    COMMAND_REG    0x0043
  14. #define WRITE_CH0    0x0036
  15. #define WRITE_CH2    0x00b6
  16. #define READ_SPECIAL    0x00c2
  17. #define    PORT_B        0x0061        /* speaker on/off control */
  18. #define    XTAL        1193182L    /* some call it 1,193,000 */
  19. #define TIMER_MODES    0x000e
  20. #define TIMER_MODE    0x0002
  21. #define TIMER_OUT    0x0080
  22. #define TIMER_PERIOD    0x0000ffffL
  23.  
  24.