50Khz PWM

[jmgelba]

18F2550
48MHz

I have set up CCP1 to provide a 50KHz PWM using the code below. However I need to use a 10bit number for the duty cycle. How do I implement that? Do I change

high_duty=(PWM_SIGNAL>>2)

to

high_duty=(PWM_SIGNAL)

and also

low_duty=(PWM_SIGNAL<<6)

to

low_duty=(PWM_SIGNAL<<8)

?

 PWM_SIGNAL = 255CCP1CON = 111100
PR2 = 239
high_duty=(PWM_SIGNAL>>2)        'high 6 bits in CCPR1L
      low_duty=(PWM_SIGNAL<<6)         'low two bits for CCP1CON
      low_duty=(low_duty>>2)           'shift back to CCP1CON<5:4>
      low_duty.3=1                     'PWM configuration bit
      low_duty.2=1                     'PWM configuration bit
CCPR1L=high_duty
CCP1CON = $0C
T2CON = 4

Thanks.

[HenrikOlsson]

Hi,
You won't get a full 10bit resolution at that frequency but it'll be pretty close. But you do

Duty VAR WORD
Duty = 500  'Or whatever

CCP1CON.4 = Duty.0
CCP1CON.5 = Duty.1
CCPR1L = (Duty >> 2)

/Henrik.

[jmgelba]

Thanks Henrik. I implemented your changes as shown below but this seems to stop the duty cycle at 25% or 256. It then rolls over to 0.

CCP1CON = %00111100
PR2 = 239
high_duty=(PWM_SIGNAL>>2)        'high 6 bits in CCPR1L
      low_duty=(PWM_SIGNAL<<6)         'low two bits for CCP1CON
      low_duty=(low_duty>>2)           'shift back to CCP1CON<5:4>
      low_duty.4=0                     'PWM configuration bit
      low_duty.5=1                     'PWM configuration bit
CCPR1L=high_duty
CCP1CON = $0C
T2CON = 4

[jmgelba]

I had PWM_SIGNAL defined as a BYTE not WORD.

Solved.