Problem with Constant Off-time PWM/Variable Frequency on dsPIC30F2020

[asaed330]

I am using a Microchip dsPIC30F2020.

I've been trying for the longest time to get some sort of PFM signal for my project. I see in Section 12.4.7 there is the ability to have constant off-time PWM - which is exactly what I want. The only condition is it has to be an external timer reset. After some reading, it seems I can use the comparator output to generate this external timer reset. However, I am getting no PWM output what so ever from the chip.

I have it set it to a programmed period of PTPER=8000 (77.6kHz). I am using CMP1A as the input to the comparator and I am using an external 0.9V voltage source to EXTREF. I have it set to independent output mode already as well. My code is attached below for guidance on what I did wrong.

I tried to model the code for my dsPIC30F2020 from the sample code from Microchip with no success. ()

What detail am I missing or did I overlook? Any help would be appreciated. Thank you.

#include "p30F2020.h"

/* Configuration Bit Settings */
_FOSCSEL(FRC_PLL)
_FOSC(CSW_FSCM_OFF & FRC_HI_RANGE & OSC2_CLKO & HS_EC_DIS)
_FWDT( FWDTEN_OFF & WINDIS_ON & WDTPRE_PR128 & WDTPOST_PS32768 )
_FPOR(PWRT_128)
_FGS( CODE_PROT_OFF & GWRP_OFF )
_FBS(BSS_NO_FLASH)

void init_PWM();
void init_CMP();

int main(void)
{
	init_PWM();					/* Initialize the PWM module */
	init_CMP();					/* Initialize the Comparator module */

  	while(1);
}

void init_PWM(void)
{
	PTPER = 8000;               /* PFM Period = 12.88 usec @ 20 MIPS for 77.6Hz */
								/* 1.61nsec for Extended */
	                            /* Refer to PWM section for more details */	
	
	MDC = 4255;					/* Constant off time of 6.55us */

	/* Initialize PWM Generator 1 */
	
	IOCON1bits.PENH		= 1;    /* PWM Module controls High output */
	IOCON1bits.PENL		= 0;    /* GPIO Module controls Low output */
	IOCON1bits.POLH		= 1;    /* High Output Polarity is active LOW */
	IOCON1bits.POLL		= 1;    /* Low Output Polarity is active LOW */
	IOCON1bits.PMOD		= 1;    /* Independent output mode */
	IOCON1bits.OVRENH 	= 0;    /* PWM generator provides data for PWM1H */
	IOCON1bits.OVRENL 	= 1;    /* OVRDAT<0> provides data for PWM1L pin */
	IOCON1bits.OVRDAT   = 0;	/* OVRENL = 1, so OVRDAT provides for PWM1L */
							
	PWMCON1bits.FLTSTAT = 0;    /* Clear Fault Interrupt flag */
	PWMCON1bits.CLSTAT = 0;     /* Clear Current Limit Interrupt flag */
	PWMCON1bits.TRGSTAT = 0;    /* Clear PWM Trigger Interrupt flag */
	PWMCON1bits.FLTIEN = 0;     /* Disable Fault Interrupt */
	PWMCON1bits.CLIEN = 1;      /* Enable Current Limit Interrupt */
	PWMCON1bits.TRGIEN = 1;     /* Enable Trigger Interrupt */
	PWMCON1bits.ITB	= 1;        /* PHASE1 provides time base period for PWM */
	PWMCON1bits.MDCS = 1;       /* Duty cycle is read from MDC */
	PWMCON1bits.DTC	= 0;        /* DTC=0: Postive dead time actively applied for all output modes */
	PWMCON1bits.XPRES = 1;      /* Current limit source resets time base for PWM1 */
	PWMCON1bits.IUE = 0;        /* Disable immediate update to PDC */

	FCLCON1bits.CLSRC = 0;		/* Current limit control signal source is comparator #1 */
	FCLCON1bits.CLMODE = 1;		/* Enable current limit mode for PWM1 */
	FCLCON1bits.CLPOL = 0;		/* Current limit polarity for PWM 1 is active HIGH */

	DTR1 = 160;					/* Deadtime = DTR1*1.61nsec = 257.6nsec */
	ALTDTR1 = 160;				/* Deadtime = ALTDTR*1.61nsec = 257.6nsec */

	PHASE1 = 0;                 /* No phase shift */

	IFS1bits.PWM1IF = 0;        /* Clear PWM1 Interrupt Flag status */
	IEC1bits.PWM1IE = 1;		/* Comparator #1 interrupt enable bit */
	
	PTCON = 0x8000;             /* Enable PWM Module */
}

void init_CMP()
{
	/* Intialize the Comparator */
	LATBbits.LATB0 = 0;			/* Initialize RB0 */
	TRISBbits.TRISB0 = 0;		/* CMP1A is an output */

	LATEbits.LATE6 = 0;			/* Initialize RE6 */
	TRISEbits.TRISE6 = 1;		/* EXTREF is an input */

	CMPCON1bits.INSEL = 0;		/* CMP1A is selected */
	CMPCON1bits.EXTREF = 1;		/* External reference for DAC. EXTREF = 0.9V */
	CMPCON1bits.CMPPOL = 0;		/* Output is not inverted */	

	CMPCON1bits.CMPON = 1;		/* Comparator module is enabled */
}

void __attribute__((interrupt, no_auto_psv)) _PWM1Interrupt()
{
	IFS1bits.PWM1IF = 0;        /* Clear PWM1 Interrupt Flag status */
}