Datasheet

© 2007 Microchip Technology Inc. DS39629C-page 151
PIC18F6390/6490/8390/8490
14.3 Compare Mode
In Compare mode, the 16-bit CCPR2 register value is
constantly compared against either the TMR1 or TMR3
register pair value. When a match occurs, the CCP2
pin can be:
• driven high
• driven low
• toggled (high-to-low or low-to-high)
• remain unchanged (that is, reflects the state of the
I/O latch)
The action on the pin is based on the value of the mode
select bits (CCP2M3:CCP2M0). At the same time, the
interrupt flag bit, CCP2IF, is set.
14.3.1 CCP PIN CONFIGURATION
The user must configure the CCPx pin as an output by
clearing the appropriate TRIS bit.
14.3.2 TIMER1/TIMER3 MODE SELECTION
Timer1 and/or Timer3 must be running in Timer mode,
or Synchronized Counter mode, if the CCP module is
using the compare feature. In Asynchronous Counter
mode, the compare operation may not work.
14.3.3 SOFTWARE INTERRUPT MODE
When the Generate Software Interrupt mode is chosen
(CCP2M3:CCP2M0 = 1010), the CCP2 pin is not
affected. Only a CCP interrupt is generated if enabled
and the CCP2IE bit is set.
14.3.4 SPECIAL EVENT TRIGGER
Both CCP modules are equipped with a Special Event
Trigger. This is an internal hardware signal generated
in Compare mode to trigger actions by other modules.
The Special Event Trigger is enabled by selecting
the Compare Special Event Trigger mode
(CCP2M3:CCP2M0 = 1011).
For either CCP module, the Special Event Trigger resets
the Timer register pair for whichever timer resource is
currently assigned as the module’s time base. This
allows the CCPRx registers to serve as a programmable
Period register for either timer.
The Special Event Trigger for CCP2 can also start an
A/D conversion. In order to do this, the A/D converter
must already be enabled.
FIGURE 14-3: COMPARE MODE OPERATION BLOCK DIAGRAM
Note: Clearing the CCP2CON register will force
the RC1 or RE7 compare output latch
(depending on device configuration) to the
default low level. This is not the PORTC or
PORTE I/O data latch.
Note: The Special Event Trigger of CCP1 only
resets Timer1/Timer3 and cannot start an
A/D conversion even when the A/D
converter is enabled.
CCPR1H CCPR1L
TMR1H TMR1L
Comparator
Q
S
R
Output
Logic
Special Event Trigger
Set CCP1IF
CCP1 pin
TRIS
CCP1CON<3:0>
Output Enable
TMR3H TMR3L
CCPR2H CCPR2L
Comparator
1
0
T3CCP2
T3CCP1
Set CCP2IF
1
0
Compare
4
(Timer1 Reset)
Q
S
R
Output
Logic
Special Event Trigger
CCP2 pin
TRIS
CCP2CON<3:0>
Output Enable
4
(Timer1/Timer3 Reset, A/D Trigger)
Match
Compare
Match