請教依下各位高手30f4011pwm範例問題

之前我從microchip的下載檔案中下載了一個範例可是其中的2小段
第1段
T1IF_Counter += 1 ;

if (T1IF_Counter > 4000)
{
T1IF_Counter = 0 ;
T1IF_Flag = 1 ;
}
IFS0bits.T1IF = 0 ;
}
void __attribute__((__interrupt__)) _PWMInterrupt(void)
{
IFS2bits.PWMIF = 0 ;
}

第2段
while (1)
{
while ( T1IF_Flag == 0 ) ;

T1IF_Flag = 0 ;

IFS0bits.T1IF = 0 ;
LATDbits.LATD0 = ! LATDbits.LATD0 ;
LATDbits.LATD1 = ! LATDbits.LATD1 ;
LATFbits.LATF0 = ! LATFbits.LATF0 ;
LATFbits.LATF1 = ! LATFbits.LATF1 ;

}
這2段我看不太懂他的作用,請各位高手幫幫忙解答一下.完整範例如下:


#define __dsPIC30F4011__

//#include <uart.h>
//#include <adc12.h>
#include <timer.h>
#include <math.h>
#include <p30F4011.h>
#include <uart.h>
#include <stdio.h>
#include "APP009V2_LCD.h"

#define pi 3.1415926
#define FCY 7372800 * 2

#define MAX_HALF_DUTY 730 // Max Duty is 180 , but multiplex with 100

#define Volt0 736

void Initial_Timer1( void ) ;
void Initial_CAN( void ) ;
void DelayNmSec(unsigned int ) ;
void InitADC10(void);
void MotPWM_Initial(void);


//---------------------------------------------------------------------------
// Configuration bits

_FOSC(CSW_FSCM_OFF & XT_PLL8); //XT with 8xPLL oscillator, Failsafe clock off
_FWDT(WDT_OFF); //Watchdog timer disabled
_FBORPOR(PBOR_OFF & MCLR_EN); //Brown-out reset disabled, MCLR reset enabled
_FGS(CODE_PROT_OFF); //Code protect disabled

typedef struct tagLEDBITS {

unsigned :8;
unsigned LED_Val:8;
} PORTDBITSS;
extern volatile PORTDBITSS LED_Ctrl __attribute__((__near__));


unsigned char TxData[10] = {0,0,0,0,0,0,0,0,0,0} ;

unsigned int ValuePDC ;

int SinTable[92] ;
int LoopVar1 ;
int U_Degree ;
int V_Degree ;
int W_Degree ;
int T1IF_Flag ;
int T1IF_Counter ;

unsigned int Temp_Uint ;

void __attribute__((__interrupt__)) _T1Interrupt(void)
{

U_Degree += 3;
if ( U_Degree > 360 ) U_Degree = 0 ;

{

if ( U_Degree <= 90 )
ValuePDC = ( SinTable[U_Degree]) + Volt0 ;

else if ( U_Degree > 90 && U_Degree <= 180 )
ValuePDC = ( SinTable[180 - U_Degree] )+ Volt0 ;

else if ( U_Degree > 180 && U_Degree <= 270 )
ValuePDC = Volt0 - ( SinTable[U_Degree - 180] ) ;

else if ( U_Degree > 270 && U_Degree <= 360 )
ValuePDC = Volt0 - ( SinTable[360-U_Degree] ) ;

PDC1 = ValuePDC ;
}

V_Degree = U_Degree + 120 ;
if ( V_Degree > 360 ) V_Degree = V_Degree - 360 ;

{
if ( V_Degree <= 90 )
ValuePDC = ( SinTable[V_Degree] )+ Volt0 ;

else if ( V_Degree > 90 && V_Degree <= 180 )
ValuePDC = ( SinTable[180 - V_Degree ] )+ Volt0 ;

else if ( V_Degree > 180 && V_Degree <= 270 )
ValuePDC = Volt0 - ( SinTable[V_Degree - 180]) ;

else if ( V_Degree > 270 && V_Degree <= 360 )
ValuePDC = Volt0 - ( SinTable[360-V_Degree] ) ;

PDC2 = ValuePDC ;
}

W_Degree = U_Degree + 240 ;
if ( W_Degree > 360 ) W_Degree = W_Degree - 360 ;

{
if ( W_Degree <= 90 )
ValuePDC = ( SinTable[W_Degree] )+ Volt0 ;

else if ( W_Degree > 90 && W_Degree <= 180 )
ValuePDC = ( SinTable[180 - W_Degree ])+ Volt0 ;

else if ( W_Degree > 180 && W_Degree <= 270 )
ValuePDC = Volt0 - ( SinTable[W_Degree - 180]) ;

else if ( W_Degree > 270 && W_Degree <= 360 )
ValuePDC = Volt0 - ( SinTable[360-W_Degree]) ;

PDC3 = ValuePDC ;
}
T1IF_Counter += 1 ;

if (T1IF_Counter > 4000)
{
T1IF_Counter = 0 ;
T1IF_Flag = 1 ;
}
IFS0bits.T1IF = 0 ;

}

void __attribute__((__interrupt__)) _PWMInterrupt(void)
{

IFS2bits.PWMIF = 0 ;
}


int main( void )

{

OpenLCD( ) ;

for ( LoopVar1 = 0 ; LoopVar1 < 91 ; LoopVar1 ++ )
{
SinTable[LoopVar1] = sin( (3.1415926 * LoopVar1) / (double)180 ) * MAX_HALF_DUTY ;
}

Initial_Timer1( ) ;
MotPWM_Initial( ) ;

TRISD &= 0x00ff ;
U_Degree = 0 ;

TRISDbits.TRISD0 = 0 ;
TRISDbits.TRISD1 = 0 ;

TRISFbits.TRISF0 = 0 ;
TRISFbits.TRISF1 = 0 ;

TRISFbits.TRISF4 = 0 ;
TRISFbits.TRISF5 = 0 ;

LATDbits.LATD0 = 0 ;
LATDbits.LATD1 = 1 ;

LATFbits.LATF0 = 0 ;
LATFbits.LATF1 = 1 ;

T1IF_Flag = 0 ;
T1IF_Counter = 0 ;

putrsLCD("dsPIC30F4011 Dem") ;
setcurLCD(0,1) ;
putrsLCD("PWM Running ") ;

while (1)
{
while ( T1IF_Flag == 0 ) ;

T1IF_Flag = 0 ;

IFS0bits.T1IF = 0 ;
LATDbits.LATD0 = ! LATDbits.LATD0 ;
LATDbits.LATD1 = ! LATDbits.LATD1 ;
LATFbits.LATF0 = ! LATFbits.LATF0 ;
LATFbits.LATF1 = ! LATFbits.LATF1 ;

}
}

void DelayNmSec(unsigned int N)
{
unsigned int j;
while(N--)
for(j=0;j < 1000;j++);
}


void Initial_Timer1( void )
{
ConfigIntTimer1( T1_INT_PRIOR_7 & T1_INT_ON ) ;
OpenTimer1( T1_ON & T1_IDLE_STOP & T1_GATE_OFF & T1_PS_1_1 & T1_SYNC_EXT_OFF & T1_SOURCE_INT ,
2048 ) ;
}

void MotPWM_Initial(void)
{
IEC2bits.PWMIE = 0 ; // Disable PWM Interrupt !!
IEC2bits.FLTAIE = 0 ;

OVDCON = 0xff00 ; // Inactive all PWM OUTPUT !!

TRISE = 0xffc0 ;
PTCON = 0xa000 ; // Configure as 0b1010 0000 0000 0000
// PWM Time Base OFF , PWM Time Base OP in free running Mode
PWMCON1 = 0x0077 ; // Configure as 0b0000000000010001
// PWM I/O in complementary Mode and only PWM1L/H as PWM output
PWMCON2 = 0x0000 ; // Configure as 0b0000000000000000

DTCON1 = 0x0101 ; // Configure as 0b0000001000000010 ;

FLTACON = 0x0000 ;

IPC9bits.PWMIP = 6 ;

// ---------------------------------------------------------------------------------
// The Switching Frequency !!
// PWM resolution >= 10 bits ,
// PDCx[1:15] compare with PTMR [0:14]
// PDCx(0) compare with MSB of prescaler counter
// So, PTPER is 9 bit if resolution of PDCx is 10 bit
// Setting PWM Frequency = 20K
// PTPER = ( (7372800*2)/ 20000 ) -1 = 736.28 = 736
// PWM Frequency will be Fcy/736 = 20.0K
// Formular !! PTPER = (Fcy/(FPWM*PTMR Prescaler)) - 1
// ---------------------------------------------------------------------------------
PTPER = 736 ; // PWM Time Base Period Register
ValuePDC = 0x00 ;

PDC1 = ValuePDC ;
PDC2 = ValuePDC ;
PDC3 = ValuePDC ;

}