Datasheet

PIC18F2585/2680/4585/4680
DS39625C-page 170 Preliminary © 2007 Microchip Technology Inc.
The ECCPR1H register and a 2-bit internal latch are
used to double-buffer the PWM duty cycle. This
double-buffering is essential for glitchless PWM
operation.
When the ECCPR1H and 2-bit latch match TMR2,
concatenated with an internal 2-bit Q clock or 2 bits of
the TMR2 prescaler, the CCP1 pin is cleared.
The maximum PWM resolution (bits) for a given PWM
frequency is given by the equation.
EQUATION 15-3:
TABLE 15-4: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 40 MHz
15.4.3 PWM AUTO-SHUTDOWN
(ECCP1 ONLY)
The PWM auto-shutdown features of the Enhanced
CCP1 module are available to ECCP1 in
PIC18F4585/4680 (40/44-pin) devices. The operation
of this feature is discussed in detail in Section 16.4.7
“Enhanced PWM Auto-Shutdown”.
Auto-shutdown features are not available for CCP1.
15.4.4 SETUP FOR PWM OPERATION
The following steps should be taken when configuring
the CCP1 module for PWM operation:
1. Set the PWM period by writing to the PR2
register.
2. Set the PWM duty cycle by writing to the
CCPR1L register and CCP1CON<5:4> bits.
3. Make the CCP1 pin an output by clearing the
appropriate TRIS bit.
4. Set the TMR2 prescale value, then enable
Timer2 by writing to T2CON.
5. Configure the CCP1 module for PWM operation.
Note: If the PWM duty cycle value is longer than
the PWM period, the ECCP1 pin will not
be cleared.
PWM Resolution (max) =
FOSC
FPWM
log
log(2)
bits
⎛
⎝
⎞
⎠
PWM Frequency 2.44 kHz 9.77 kHz 39.06 kHz 156.25 kHz 312.50 kHz 416.67 kHz
Timer Prescaler (1, 4, 16)1641111
PR2 Value FFh FFh FFh 3Fh 1Fh 17h
Maximum Resolution (bits) 14 12 10 8 7 6.58