hardware_delay_50ms.c

keil C51 50ms事例

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

   Hardware_Delay_50ms.C (v1.00)

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

   A test program for hardware-based delays.

   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>

sbit LED_pin = P1^5;
bit LED_state_G;

void LED_FLASH_Init(void);
void LED_FLASH_Change_State(void);

void DELAY_HARDWARE_One_Second(void);
void DELAY_HARDWARE_50ms(void);

/*..................................................................*/

void main(void)
   {
   LED_FLASH_Init();

   while(1) 
      {
      // Change the LED state (OFF to ON, or vice versa)
      LED_FLASH_Change_State();

      // Delay for approx 1000 ms
      DELAY_HARDWARE_One_Second();
      }   
   }

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

  LED_FLASH_Init()

  Prepare for LED_Change_State() function - see below.

-*------------------------------------------------------------------*/
void LED_FLASH_Init(void)
   {
   LED_state_G = 0;
   }


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

  LED_FLASH_Change_State()

  Changes the state of an LED (or pulses a buzzer, etc) on a 
  specified port pin.

  Must call at twice the required flash rate: thus, for 1 Hz
  flash (on for 0.5 seconds, off for 0.5 seconds) must call
  every 0.5 seconds.

-*------------------------------------------------------------------*/
void LED_FLASH_Change_State(void)
   {
   // Change the LED from OFF to ON (or vice versa)
   if (LED_state_G == 1)
      {
      LED_state_G = 0;
      LED_pin = 0;
      }
   else
      {
      LED_state_G = 1;
      LED_pin = 1;
      }
   }

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

  DELAY_HARDWARE_One_Second()

  Hardware delay of 1000 ms.  

  *** Assumes 12MHz 8051 (12 osc cycles) ***

-*------------------------------------------------------------------*/
void DELAY_HARDWARE_One_Second(void)
   {
   unsigned char d;

   // Call DELAY_HARDWARE_50ms() twenty times
   for (d = 0; d < 20; d++)
      {
      DELAY_HARDWARE_50ms();
      }     
   }

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

  DELAY_HARDWARE_50ms()

  Hardware delay of 50ms.  

  *** Assumes 12MHz 8051 (12 osc cycles) ***

-*------------------------------------------------------------------*/
void DELAY_HARDWARE_50ms(void)
   {
   // Configure Timer 0 as a 16-bit timer 
   TMOD &= 0xF0; // Clear all T0 bits (T1 left unchanged)
   TMOD |= 0x01; // Set required T0 bits (T1 left unchanged) 

   ET0 = 0;  // No interupts

   // Values for 50 ms delay
   TH0 = 0x3C;  // Timer 0 initial value (High Byte)
   TL0 = 0xB0;  // Timer 0 initial value (Low Byte)

   TF0 = 0;          // Clear overflow flag
   TR0 = 1;          // Start timer 0
   while (TF0 == 0); // Loop until Timer 0 overflows (TF0 == 1)
   
   TR0 = 0;         // Stop Timer 0
  		}

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