f36x_oscillator_crystal.c

芯科原厂所有c8051fxx程序的例子。

//-----------------------------------------------------------------------------
// F36x_Oscillator_Crystal.c
//-----------------------------------------------------------------------------
// Copyright 2006 Silicon Laboratories, Inc.
// http://www.silabs.com
//
// Program Description:
//
// This program demonstrates how to configure the oscillator for use with an
// external quartz crystal.
//
//
// How To Test:
//
// 1) Ensure that a quartz crystal, 10Meg resistor, and 33pF loading capacitors
//    are installed.
// 1) Define the input external crystal frequency using <Crystal_Clock>
// 2) Compile and download code to a 'F36x device.
// 3) Run the code:
//      - the test will blink an LED at a frequency based on the External
//         Crystal frequency
//      - the 'F36x will also output the SYSCLK to a port pin (P0.0) for
//         observation
//
//
// FID:            36X000017
// Target:         C8051F36x
// Tool chain:     Keil C51 7.50 / Keil EVAL C51
// Command Line:   None
//
// Release 1.0
//    -Initial Revision (FB / TP)
//    -25 OCT 2006
//

//-----------------------------------------------------------------------------
// Includes
//-----------------------------------------------------------------------------

#include <C8051F360.h>                 // SFR declarations

//-----------------------------------------------------------------------------
// External Oscillator Crystal Frequency Selection
//-----------------------------------------------------------------------------
//
// Please initialize the following constant to the crystal frequency
//
#define Crystal_Clock 22118400L        // External Crystal oscillator
                                       // frequency (Hz)
                                       // NOTE: This value will determine the
                                       // XFCN bits in ExtCrystalOsc_Init ()

// Timer2 using SYSCLK/12 as its time base
// Timer2 counts 65536 SYSCLKs per Timer2 interrupt
// LED target flash rate = 10 Hz
//
// If Crystal_Clock is too slow to divide into a number of counts,
// <count> will always remain 0.
#define LED_interrupt_count Crystal_Clock/12/65536/10

//-----------------------------------------------------------------------------
// 16-bit Register Definitions for the 'F36x
//-----------------------------------------------------------------------------

sfr16 TMR2RL = 0xCA;                   // Timer2 reload value
sfr16 TMR2 = 0xCC;                     // Timer2 counter

//-----------------------------------------------------------------------------
// Global Variables
//-----------------------------------------------------------------------------

sbit LED = P3^2;                       // LED='1' means ON

//-----------------------------------------------------------------------------
// Function Prototypes
//-----------------------------------------------------------------------------

void SYSCLK_Init (void);
void ExtCrystalOsc_Init (void);
void Port_Init (void);
void Timer2_Init (void);

//-----------------------------------------------------------------------------
// main() Routine
//-----------------------------------------------------------------------------

void main (void)
{
   PCA0MD &= ~0x40;                    // WDTE = 0 (clear watchdog timer
                                       // enable)

   Port_Init ();                       // Initialize crossbar and GPIO

   SYSCLK_Init ();                     // Initialize system clock to 24.5MHz

   ExtCrystalOsc_Init ();              // Initialize for and switch to the
                                       // external Crystal oscillator

   Timer2_Init ();                     // Init Timer2 to generate
                                       // interrupts for the LED.

   EA = 1;                             // Enable global interrupts

   SFRPAGE = LEGACY_PAGE;

   while (1) {};                       // Loop forever

}                                      // End of main()

//-----------------------------------------------------------------------------
// Initialization Subroutines
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// SYSCLK_Init ()
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This routine initializes the system clock to use the internal 24.5 MHz
// oscillator as its clock source.  Also enables missing clock detector reset.
//
void SYSCLK_Init (void)
{
   unsigned char SFRPAGE_save = SFRPAGE; // Save the current SFRPAGE

   SFRPAGE = CONFIG_PAGE;              // Switch to the necessary SFRPAGE

   OSCICN |= 0x03;                     // Configure internal oscillator for
                                       // its highest frequency (16 MHz)

   RSTSRC = 0x04;                      // Enable missing clock detector

   SFRPAGE = SFRPAGE_save;             // Restore the SFRPAGE
}

//-----------------------------------------------------------------------------
// ExtCrystalOsc_Init ()
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This routine initializes for and switches to the External Crystal
// Oscillator.
//
void ExtCrystalOsc_Init (void)
{
   unsigned int i;
   unsigned char SFRPAGE_save = SFRPAGE; // Save the current SFRPAGE

   SFRPAGE = CONFIG_PAGE;              // Switch to the necessary SFRPAGE

   // Set the appropriate XFCN bits for the crystal frequency
   //
   //   XFCN     Crystal (XOSCMD = 11x)
   //   000      f <= 32 kHz
   //   001      32 kHz < f <= 84 kHz
   //   010      84 kHz < f <= 225 kHz
   //   011      225 kHz < f <= 590 kHz
   //   100      590 kHz < f <= 1.5 MHz
   //   101      1.5 MHz < f <= 4 MHz
   //   110      4 MHz < f <= 10 MHz
   //   111      10 MHz < f <= 30 MHz
   #if (Crystal_Clock <= 32000)
      #define XFCN 0
   #elif (Crystal_Clock <= 84000L)
      #define XFCN 1
   #elif (Crystal_Clock <= 225000L)
      #define XFCN 2
   #elif (Crystal_Clock <= 590000L)
      #define XFCN 3
   #elif (Crystal_Clock <= 1500000L)
      #define XFCN 4
   #elif (Crystal_Clock <= 4000000L)
      #define XFCN 5
   #elif (Crystal_Clock <= 10000000L)
      #define XFCN 6
   #elif (Crystal_Clock <= 30000000L)
      #define XFCN 7
   #else
      #error "Defined Crystal Frequency outside allowable range!"
      #define XFCN 0
   #endif

   // Step 1. Enable the external oscillator.
   OSCXCN = 0x60;                      // External Oscillator is an external
                                       // crystal (no divide by 2 stage)

   OSCXCN |= XFCN;


   // Step 2. Wait at least 1 ms.
   for (i = 12250; i > 0; i--);        // At 24.5 MHz, 1 ms = 24500 SYSCLKs
                                       // DJNZ = 2 SYSCLKs


   // Step 3. Poll for XTLVLD =>