Datasheet

PIC18F87J72 FAMILY
DS39979A-page 158 Preliminary  2010 Microchip Technology Inc.
16.1 CCP Module Configuration
Each Capture/Compare/PWM module is associated
with a control register (generically, CCPxCON) and a
data register (CCPRx). The data register, in turn, is
comprised of two 8-bit registers: CCPRxL (low byte)
and CCPRxH (high byte). All registers are both
readable and writable.
16.1.1 CCP MODULES AND TIMER
RESOURCES
The CCP modules utilize timers, 1, 2 or 3, depending
on the mode selected. Timer1 and Timer3 are available
to modules in Capture or Compare modes, while
Timer2 is available for modules in PWM mode.
TABLE 16-1: CCP MODE – TIMER
RESOURCE
The assignment of a particular timer to a module is
determined by the Timer to CCP enable bits in the
T3CON register (Register 14-1). Both modules may be
active at any given time and may share the same timer
resource if they are configured to operate in the same
mode (Capture/Compare or PWM) at the same time.
The interactions between the two modules are
summarized in Table 16-2.
Depending on the configuration selected, up to four
timers may be active at once, with modules in the same
configuration (Capture/Compare or PWM) sharing
timer resources. The possible configurations are
shown in Figure 16-1.
16.1.2 OPEN-DRAIN OUTPUT OPTION
When operating in Output mode (i.e., in Compare or
PWM modes), the drivers for the CCPx pins can be
optionally configured as open-drain outputs. This
feature allows the voltage level on the pin to be pulled
to a higher level through an external pull-up resistor
and allows the output to communicate with external
circuits without the need for additional level shifters.
The open-drain output option is controlled by the
CCP2OD and CCP1OD bits (TRISG<6:5>). Setting the
appropriate bit configures the pin for the corresponding
module for open-drain operation.
16.1.3 CCP2 PIN ASSIGNMENT
The pin assignment for CCP2 (capture input, compare
and PWM output) can change, based on device config-
uration. The CCP2MX Configuration bit determines
which pin CCP2 is multiplexed to. By default, it is
assigned to RC1 (CCP2MX = 1). If the Configuration bit
is cleared, CCP2 is multiplexed with RE7.
Changing the pin assignment of CCP2 does not
automatically change any requirements for configuring
the port pin. Users must always verify that the appropri-
ate TRIS register is configured correctly for CCP2
operation, regardless of where it is located.
FIGURE 16-1: CCP AND TIMER INTERCONNECT CONFIGURATIONS
CCP Mode Timer Resource
Capture
Compare
PWM
Timer1 or Timer3
Timer1 or Timer3
Timer2
TMR1
TMR2
TMR3
CCP2
CCP1
TMR1
TMR2
TMR3
CCP2
CCP1
TMR1 TMR3
TMR2
CCP2
CCP1
T3CCP<2:1> = 00 T3CCP<2:1> = 01 T3CCP<2:1> = 1x
Timer1 is used for all capture
and compare operations for
all CCP modules. Timer2 is
used for PWM operations for
all CCP modules. Modules
may share either timer
resource as a common time
base.
Timer1 is used for capture
and compare operations for
CCP1 and Timer 3 is used for
CCP2.
Both the modules use Timer2
as a common time base if they
are in PWM modes.
Timer3 is used for all capture
and compare operations for
all CCP modules. Timer2 is
used for PWM operations for
all CCP modules. Modules
may share either timer
resource as a common time
base.