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Sine wave

Andrew Jordan

Hi

I have found the codes and I am trying to understand the code as it is about generating sine wave but I got lost in the offset sections.

I would be grateful if you offer any help me to understand the codes as shown below:

In fact I would expect the PWM frequency should be 5kHz and the frequency modulation - 400Hz



// Timer 0 & 1 - Timer mode (Non-staggered)
// T0I - 000 hence prescaler would be 1, period = 1.6384ms
// T1I - 111 hence prescaler would be 128, period = 209.72ms

CC1_T01CON     =  0x0700;


//  Since I don't know what is the desired period for timer 0 & reload (0XF060)
//  Hence 61536=(DESIRED PERIOD/1.6384E-3)*65536
//  DESIRED PERIOD would be 1.5384e-3 (650Hz)

C1_T0         =  0xF060;

CC1_T0REL      =  0xF060;

// CAPCOM1 : CC1_CC2/3 ARE ALLOCATED TO TIMER TO
// 	   : Mode 3 are set for CC2 and CC3

CC1_M0         =  0x7700;


ALTSEL0P6     |=  0x003C;      			// select alternate output function
DP6  = (DP6  & ~(uword)0x003C) | 0x003C;    	//set direction register


// Enable the CAPCOM1 Timer

CC1_T01CON_T0R    = 1;    // set CAPCOM1 timer 0 run bit

// Obtain the offset but I don't understand the reason behind this method

offset = (0xFFFF - CC1_T0REL)>>1;

// Generating look up table for sine wave

TempFloat = TABLE_SIZE;			// 50
TempFloat = (360)/TempFloat;	// Get the increment size for the sine wave look up table


for (loopcount=0; loopcount<TABLE_SIZE; loopcount++){
	SineWave[loopcount]=(offset*sin(((loopcount*TempFloat)*3.14159)/180));
    }

//  I don't why offset is added to CC1_TOREL (Can anyone care to explain reason behind this?)

	CC1_CC2 = CC1_T0REL + offset;
	CC1_CC3 = CC1_T0REL + offset;
	CC1_CC2_Temp = CC1_CC2;
	CC1_CC3_Temp = CC1_CC3;

//  Can anyone please tell me what _sof_ is for?

  SRCP5  =  _sof_(&CC1_CC2_Temp);
  SRCP6  =  _sof_(&CC1_CC3_Temp);



Interrupt routine for CC1_T0INT


	int TempInt;
	long int TempLong;



		pwm_ref++;

		if(pwm_ref >= 50){
			pwm_ref = 0;
			}


		TempLong = 5000;			// amplitude
		TempLong = SineWave[pwm_ref]*TempLong;
		TempInt = (TempLong)/10000;

		//  Can someone please please tell me what is the hell is going on epecially two last codes
		//

		CC1_CC2_Temp = CC1_T0REL + (offset + TempInt);	// apply sine wave
		CC1_CC3_Temp = CC1_T0REL + (offset - TempInt);	// apply sine wave

AJ

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