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DS80000533H-page  14

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In Center-Aligned Complementary mode with 
Independent Time Base, the PWM generator may 
assert the PWMxH output for 100% of the duty 
cycle. This has been observed when the value in 
its PDCx register is less than one-half the value in 
its ALTDTRx register. 

Include a software routine to check that the duty 
cycle value written to the PDCx register is always 
at least one-half of the value in ALTDTRx. 

 shows one way of doing this, with 

PDCtemp

 representing the value to be written to 

the PDCx register.

This issue is applicable when a PWM generator is 
configured to operate in Independent Time Base 
mode with either Center-Aligned Complementary 
mode or Edge-Aligned Complementary mode. 
When dead time is non-zero, PWMxL is not 
asserted for 100% of the time when PDCx is zero. 
Similarly, when dead time is non-zero, PWMxH is 
not asserted for 100% of the time when PDCx is 
equal to PHASEx. This issue applies to Master 
Time Base mode as well.

In Center-Aligned mode:

• To obtain 0% duty cycle, first zero out the 

ALTDTRx register, then write zero to the 
PDCx register.

• To obtain 100% duty cycle, first zero out the 

ALTDTRx register, then write (PHASEx + 2) to 
the PDCx register.

In Edge-Aligned mode:

• To obtain 0% duty cycle, first zero out the 

registers, DTRx and ALTDTRx, then write 
zero to the PDCx register.

• To obtain 100% duty cycle, first zero out the 

registers, DTRx and ALTDTRx, then write 
(PHASEx + 1) to the PDCx register.

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—

Altdtr_by2 = ALTDTRx / 2;

if

(PDCtemp < Altdtr_by2)

{

PDCx = Altdtr_by2;

}

else

{

PDCx = PDCtemp;

}

dsPIC33/PIC24EP32 devices

dsPIC33/PIC24EP64 devices

dsPIC33/PIC24EP128 devices

dsPIC33/PIC24EP256 devices

dsPIC33/PIC24EP512 devices