PIC18F2220/2320/4220/4320
waveforms do not exactly match the standard PWM
waveforms but are instead offset by one full instruction
cycle (4 TOSC).
16.4 Enhanced PWM Mode
The Enhanced PWM mode provides additional PWM
output options for a broader range of control applica-
tions. The module is an upwardly compatible version of
the standard CCP module and offers up to four outputs,
designated P1A through P1D. Users are also able to
select the polarity of the signal (either active-high or
active-low). The module’s output mode and polarity are
configured by setting the P1M1:P1M0 and
CCP1M3:CCP1M0 bits of the CCP1CON register
(CCP1CON<7:6> and CCP1CON<3:0>, respectively).
As before, the user must manually configure the
appropriate TRISD bits for output.
16.4.1
PWM OUTPUT CONFIGURATIONS
The P1M1:P1M0 bits in the CCP1CON register allow
one of four configurations:
• Single Output
• Half-Bridge Output
Figure 16-1 shows a simplified block diagram of PWM
operation. All control registers are double-buffered and
are loaded at the beginning of a new PWM cycle (the
period boundary when Timer2 resets) in order to pre-
vent glitches on any of the outputs. The exception is the
PWM Delay register, ECCP1DEL, which is loaded at
either the duty cycle boundary or the boundary period
(whichever comes first). Because of the buffering, the
module waits until the assigned timer resets instead of
starting immediately. This means that enhanced PWM
• Full-Bridge Output, Forward mode
• Full-Bridge Output, Reverse mode
The Single Output mode is the Standard PWM mode
discussed in Section 15.5 “PWM Mode”. The Half-
Bridge and Full-Bridge Output modes are covered in
detail in the sections that follow.
The general relationship of the outputs in all
configurations is summarized in Figure 16-2.
FIGURE 16-1:
SIMPLIFIED BLOCK DIAGRAM OF THE ENHANCED PWM MODULE
CCP1CON<5:4>
P1M1<1:0>
CCP1M<3:0>
4
Duty Cycle Registers
2
CCPR1L
CCP1/P1A
RC2/CCP1/P1A
TRISD<4>
TRISD<5>
TRISD<6>
TRISD<7>
CCPR1H (Slave)
Comparator
P1B
RD5/PSP5/P1B
RD6/PSP6/P1C
Output
Controller
R
S
Q
P1C
(Note 1)
TMR2
P1D
RD7/PSP7/P1D
Comparator
PR2
Clear Timer,
set CCP1 pin and
latch D.C.
PWM1CON
Note: The 8-bit timer TMR2 register is concatenated with the 2-bit internal Q clock or 2 bits of the prescaler to create the 10-bit time base.
2003 Microchip Technology Inc.
DS39599C-page 143
MICROCHIP [ MICROCHIP ]
