Solenoid PWM

;******************************************************************
;
;  //  setup a 1000 usec PWM period with PR2 = 249 and prescaler
;  //  4:1 (4 MHz clock) or 16:1 (16-MHz clock) and use 25 of
;  //  these shorter PWM "frames" to make the much longer 25-msec
;  //  period.  Resolution is 1-usec.
;
;  int width = 1500;              // pulse width, 0..24999 (usecs)
;  int pulse = 0;                 // ISR work variable
;  int frame = 1;                 // frame number 1..25
;
;  void ISR()
;  { PIR1bits.TMR2IF = 0;         // clear Timer 2 interrupt flag
;    frame--;                     // decrement frame number
;    if (frame == 0)              // if end of 25 msec period
;    { frame = 25;                // reset for new 25 msec period
;      pulse = width;             // reset 'pulse' work variable
;    }
;    if ((pulse > 1000)           // if pulse > 1000 usecs
;    { CCPR1L = 250;              // do a 100% duty cycle frame
;      CCP1CONbits.CCP1Y = 0;     //
;      CCP1CONbits.CCP1X = 0;     //
;      pulse -= 1000;             // subtract 1000 usecs
;    }
;    else
;    { CCP1CONbits.CCP1Y = (pulse & 1);
;      CCP1CONbits.CCP1X = (pulse & 2);
;      CCPR1L = (pulse >> 2);     // 0..249 (0..999 usecs)
;      pulse = 0;                 // remaining frames are 0%
;    }
;  }