hardware_delay_50ms.c

Embedded C 这本书的范例光碟程式

/*------------------------------------------------------------------*-
   Hardware_Delay_50ms.C (v1.00)
  ------------------------------------------------------------------*/

#include <reg52.h>

sbit LED_pin = P1^0;
 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) 
   {
      LED_FLASH_Change_State();      // Change the LED state (OFF to ON, or vice versa)
      DELAY_HARDWARE_One_Second();   // Delay for approx 1000 ms
   }   
}

/*----------------------------------------------------------------
  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;

   for (d = 0; d < 10; d++)   // Call DELAY_HARDWARE_50ms() twenty times
   {
      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
}