Re: Changing the Duty Cycle

[CJO]

In a message posted in the easyC forum, someone askes if there was a way of changing the duty cycle (and presumably other) charactetristics of the PWM outputs.

The response was the this was not possible in easyC or in regular C (MPLAB).

I am pretty sure that it is, in fact, possible to change the PWMs. From RKW’s Serial Ports Codebase (v .3 – the current version)

@user_routines.c

/*******************************************************************************

• FUNCTION NAME: Setup_Who_Controls_Pwms
• PURPOSE: Each parameter specifies what processor will control the pwm.
• CALLED FROM: User_Initialization

• Argument             Type    IO   Description
  

• --------             ----    --   -----------
  

• pwmSpec1              int     I   USER/MASTER (defined in ifi_aliases.h)
  

• pwmSpec2              int     I   USER/MASTER
  

• pwmSpec3              int     I   USER/MASTER
  

• pwmSpec4              int     I   USER/MASTER
  

• pwmSpec5              int     I   USER/MASTER
  

• pwmSpec6              int     I   USER/MASTER
  

• pwmSpec7              int     I   USER/MASTER
  

• pwmSpec8              int     I   USER/MASTER
  

• RETURNS: void
  ******************************************************************************/
  static void Setup_Who_Controls_Pwms(int pwmSpec1,int pwmSpec2,int pwmSpec3,int pwmSpec4,
  int pwmSpec5,int pwmSpec6,int pwmSpec7,int pwmSpec8)
  {
  txdata.pwm_mask = 0xFF; / Default to master controlling all PWMs. /
  if (pwmSpec1 == USER) / If User controls PWM1 then clear bit0. /
  txdata.pwm_mask &= 0xFE; / same as txdata.pwm_mask = txdata.pwm_mask & 0xFE; /
  if (pwmSpec2 == USER) / If User controls PWM2 then clear bit1. /
  txdata.pwm_mask &= 0xFD;
  if (pwmSpec3 == USER) / If User controls PWM3 then clear bit2. /
  txdata.pwm_mask &= 0xFB;
  if (pwmSpec4 == USER) / If User controls PWM4 then clear bit3. /
  txdata.pwm_mask &= 0xF7;
  if (pwmSpec5 == USER) / If User controls PWM5 then clear bit4. /
  txdata.pwm_mask &= 0xEF;
  if (pwmSpec6 == USER) / If User controls PWM6 then clear bit5. /
  txdata.pwm_mask &= 0xDF;
  if (pwmSpec7 == USER) / If User controls PWM7 then clear bit6. /
  txdata.pwm_mask &= 0xBF;
  if (pwmSpec8 == USER) / If User controls PWM8 then clear bit7. */
  txdata.pwm_mask &= 0x7F;
  }

And further down in the same file:

@user_routines.c

/* EIGHTH: Set your PWM output type. Only applies if USER controls PWM 1, 2, 3, or 4. /
/ Choose from these parameters for PWM 1-4 respectively: /
/ IFI_PWM - Standard IFI PWM output generated with Generate_Pwms(…) /
/ USER_CCP - User can use PWM pin as digital I/O or CCP pin. */
Setup_PWM_Output_Type(IFI_PWM,IFI_PWM,IFI_PWM,IFI_PWM);

/*
Example: The following would generate a 40KHz PWM with a 50% duty cycle
on the CCP2 pin (PWM OUT 1):
CCP2CON = 0x3C;
PR2 = 0xF9;
CCPR2L = 0x7F;
T2CON = 0;
T2CONbits.TMR2ON = 1;
Setup_PWM_Output_Type(USER_CCP,IFI_PWM,IFI_PWM,IFI_PWM);
*/

I m on the road at the moment, and do not have ready access to some of my workspaces, but I am pretty sure that I have done this before.

~ Christopher