switch_read.c

keil C51 Switch事例

/*------------------------------------------------------------------*-

   Switch_read.C (v1.00)

  ------------------------------------------------------------------

   A simple 'switch input' program for the 8051.
   - Reads (and debounces) switch input on Pin1^0
   - If switch is pressed, changes Port 3 output.


   COPYRIGHT
   ---------

   This code is associated with the book:

   EMBEDDED C by Michael J. Pont 
   [Pearson Education, 2002: ISBN: 0-201-79523-X].

   This code is copyright (c) 2001 by Michael J. Pont.
 
   See book for copyright details and other information.

-*------------------------------------------------------------------*/

#include <reg52.h>

// Connect switch to this pin
sbit Switch_pin = P1^0;

// Display switch status on this port
#define Output_port P3

// Return values from Switch_Get_Input()
#define SWITCH_NOT_PRESSED (bit) 0 
#define SWITCH_PRESSED (bit) 1 

// Function prototypes
void SWITCH_Init(void);
bit  SWITCH_Get_Input(const unsigned char); 
void DISPLAY_SWITCH_STATUS_Init(void);
void DISPLAY_SWITCH_STATUS_Update(const bit);
void DELAY_LOOP_Wait(const unsigned int);

/* ---------------------------------------------------------------- */
void main(void)
   {
   bit Sw_state;

   // Init functions
   SWITCH_Init();
   DISPLAY_SWITCH_STATUS_Init();
  
   while(1) 
      {
      Sw_state = SWITCH_Get_Input(30);
       
      DISPLAY_SWITCH_STATUS_Update(Sw_state);
      }
   }

/*------------------------------------------------------------------*-

  SWITCH_Init()

  Initialization function for the switch library.

-*------------------------------------------------------------------*/
void SWITCH_Init(void)
   {
   Switch_pin = 1; // Use this pin for input
   }

/*------------------------------------------------------------------*-
  
  SWITCH_Get_Input()

  Reads and debounces a mechanical switch as follows:

  1. If switch is not pressed, return SWITCH_NOT_PRESSED.

  2. If switch is pressed, wait for DEBOUNCE_PERIOD (in ms).
     a. If switch is not pressed, return SWITCH_NOT_PRESSED. 
     b. If switch is pressed, wait (indefinitely) for
        switch to be released, then return SWITCH_PRESSED

  See Switch_Wait.H for details of return values.
  
-*------------------------------------------------------------------*/
bit SWITCH_Get_Input(const unsigned char DEBOUNCE_PERIOD)
   {
   bit Return_value = SWITCH_NOT_PRESSED;

   if (Switch_pin == 0)
      {
      // Switch is pressed
      
      // Debounce - just wait...
      DELAY_LOOP_Wait(DEBOUNCE_PERIOD);

      // Check switch again
      if (Switch_pin == 0)
         {
         Return_value = SWITCH_PRESSED;
         }
      }
   
   // Now return switch value
   return Return_value;
   }

/*------------------------------------------------------------------*-

  DISPLAY_SWITCH_STATUS_Init()

  Initialization function for the DISPLAY_SWITCH_STATUS library.

-*------------------------------------------------------------------*/
void DISPLAY_SWITCH_STATUS_Init(void)
   {
   Output_port = 0xF0;
   }

/*------------------------------------------------------------------*-

  DISPLAY_SWITCH_STATUS_Update()

  Simple function to display data (SWITCH_STATUS) 
  on LEDs connected to port (Output_Port)

-*------------------------------------------------------------------*/
void DISPLAY_SWITCH_STATUS_Update(const bit SWITCH_STATUS)
   {
   if (SWITCH_STATUS == SWITCH_PRESSED)
      {
      Output_port = 0x0F;
      }
   else
      {
      Output_port = 0xF0;
      }
   } 

/*------------------------------------------------------------------*-

  DELAY_LOOP_Wait()

  Delay duration varies with parameter.  

  Parameter is, *ROUGHLY*, the delay, in milliseconds,
  on 12MHz 8051 (12 osc cycles).

  You need to adjust the timing for your application!

-*------------------------------------------------------------------*/
void DELAY_LOOP_Wait(const unsigned int DELAY_MS)
   {
   unsigned int x, y;

   for (x = 0; x <= DELAY_MS; x++)
      {
      for (y = 0; y <= 120; y++);
      }
   }


/*------------------------------------------------------------------*-
  ---- END OF FILE -------------------------------------------------
-*------------------------------------------------------------------*/