f32x_clock_multiplier.c

8051 Clock_Multiplier 用於8051之OSC應用

//-----------------------------------------------------------------------------
// F32x_Clock_Multiplier.c
//-----------------------------------------------------------------------------
// Copyright 2006 Silicon Laboratories, Inc.
// http://www.silabs.com
//
// Program Description:
//
// This example demonstrates how to initialize and switch to the C8051F32x
// Clock Multiplier.
// - Pinout:
//    P2.0 -> SW
//
//    P2.2 -> LED
//
//    P3.0 -> C2D (debug interface)
//
//    all other port pins unused
//
// How To Test:
//
// 1) Download code to a 'F32x device.
// 2) Verify that the P2.2 -> P2.2_LED is in place on the J3 header.
// 3) Run the code:
//      - the test will blink an LED at a frequency based on the SYSCLK
//      - press the switch on P2.0 to switch the SYSCLK between the internal
//        oscillator (12 MHz) and the Clock Multiplier/2 (24 MHz).
//
//
// FID:            32X000052
// Target:         C8051F32x
// Tool chain:     Keil C51 7.50 / Keil EVAL C51
// Command Line:   None
//
// Release 1.0
//    -Initial Revision (TP)
//    -24 MAY 2006
//

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

#include <C8051F320.h>                 // SFR declarations

//-----------------------------------------------------------------------------
// Global CONSTANTS
//-----------------------------------------------------------------------------

#define init_SYSCLK 12000000           // Initial SYSCLK setting = IntOsc

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

sbit LED = P2^2;                       // LED='1' means ON
sbit SW = P2^0;                        // SW='0' means switch pressed

//-----------------------------------------------------------------------------
// Function PROTOTYPES
//-----------------------------------------------------------------------------

void SYSCLK_Init (void);
void CLKMUL_Init (void);
void Port_Init (void);
void Timer2_Init (void);

void Timer2_ISR (void);

//-----------------------------------------------------------------------------
// MAIN Routine
//-----------------------------------------------------------------------------
//
// Main routine performs all configuration tasks, then loops forever polling on
// the SW switch and switching the CLKSEL register between the Internal
// Oscillator and the Clock Multiplier/2.
//
//-----------------------------------------------------------------------------
void main (void) 
{
   PCA0MD &= ~0x40;                    // WDTE = 0 (clear watchdog timer
                                       // enable)

   SYSCLK_Init ();                     // Initialize system clock to 12MHz

   CLKMUL_Init ();                     // Initialize the Clock Multiplier

   Port_Init ();                       // Initialize crossbar and GPIO
   Timer2_Init ();                     // Init Timer2 to generate
                                       // interrupts for the LED.
                                       // When the SYSCLK is switched to
                                       // the Clock Multiplier output, the
                                       // interrupts will be at 2x the rate.

   EA = 1;                             // Enable global interrupts

   while (1) {                         // Spin forever

      while (SW != 0);                 // Wait until the switch is pressed

      CLKSEL = 0x02;                   // Switch SYSCLK to the CLKMUL output
                                       // LED now blinking at 2x the rate

      while (SW == 0);                 // Wait until the switch is released



      while (SW != 0);                 // Wait until the switch is pressed

      CLKSEL = 0x00;                   // Switch SYSCLK to the IntOsc output
                                       // LED now blinking at the original
                                       // rate

      while (SW == 0);                 // Wait until the switch is released
   }
}

//-----------------------------------------------------------------------------
// Initialization Routines
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// SYSCLK_Init ()
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This routine initializes the system clock to use the internal 12 MHz
// oscillator as its clock source.  Also enables missing clock detector reset.
//
//-----------------------------------------------------------------------------
void SYSCLK_Init (void)
{
   OSCICN = 0x83;                      // Configure internal oscillator for
                                       // its highest frequency (12 MHz)

   RSTSRC = 0x04;                      // Enable missing clock detector
}

//-----------------------------------------------------------------------------
// CLKMUL_Init ()
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This routine initializes the Clock Multiplier using the Internal Oscillator
// as the source.
//
//-----------------------------------------------------------------------------
void CLKMUL_Init (void)
{
   char i;

   CLKMUL = 0x00;                      // Reset the Multiplier by writing 0x00
                                       // to register CLKMUL.

   CLKMUL |= 0x00;                     // Select the Multiplier input source
                                       // via the MULSEL bits.
                                       // '00'b = Internal Oscillator

   CLKMUL |= 0x80;                     // Enable the Multiplier with the MULEN
                                       // bit (CLKMUL | = 0x80).

   for (i = 35; i > 0; i--);           // Delay for >5 祍.
                                       // At 12 MHz SYSCLK ~ 80 ns, so 5 us is
                                       // 61 SYSCLK counts. DJNZ = 2 clocks.

   CLKMUL |= 0xC0;                     // Initialize the Multiplier with the
                                       // MULINIT bit (CLKMUL | = 0xC0).

   while ((CLKMUL & 0x20) != 0x20);    // Poll for MULRDY =>