1995 Microchip Technology Inc.
DS30390B-page 73
PIC16C7X
10.1.1
PRESCALER
There are four prescaler settings, specified by bits
CCP1M3:CCP1M0. Whenever the CCP module is
turned off, or the CCP module is not in capture mode,
the prescaler counter is cleared. This means that any
reset will clear the prescaler counter.
Switching from one capture prescaler to another may
generate an interrupt. Also, the prescaler counter will
not be cleared, therefore the first capture may be from
a non-zero prescaler. Example 10-1 shows the recom-
mended method for switching between capture pres-
calers. This example also clears the prescaler counter
and will not generate the “false” interrupt.
EXAMPLE 10-1: CHANGING BETWEEN
CAPTURE PRESCALERS
CLRF CCP1CON ;Turn CCP module off
MOVLW NEW_CAPT_PS ;Load the W reg with
; the new prescaler
; mode value and CCP ON
MOVWF CCP1CON ;Load CCP1CON with this
; value
10.1.2
CAPTURE MODE SELECTION
Timer1 must be running in timer mode or synchronized
counter mode for the CCP module to use the capture
feature. In asynchronous counter mode, the capture
operation may not work.
FIGURE 10-2: CAPTURE MODE
OPERATION BLOCK
DIAGRAM
10.2
Compare Mode
Applicable Devices
70 71 71A 72 73 73A 74 74A
In Compare mode, the 16-bit CCPR1 register value is
constantly compared against the TMR1 register pair
value. When a match occurs, the RC2/CCP1 pin is:
Driven High
Driven Low
Remains Unchanged
CCPR1H
CCPR1L
TMR1H
TMR1L
Set flag bit CCP1IF
(PIR1<2>)
Capture
Enable
Q’s
CCP1CON<3:0>
RC2/CCP1
Pin
Prescaler
÷
1, 4, 16
and
edge detect
The action on the pin is based on the value of control
bits CCP1M3:CCP1M0 (CCP1CON<3:0>). At the
same time, a compare interrupt is also generated. The
user must configure the RC2/CCP1 pin as an output by
clearing the TRISC<2> bit.
10.2.1
COMPARE MODE SELECTION
Timer1 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.
10.2.2
SOFTWARE INTERRUPT MODE
Another compare mode is software interrupt mode in
which the CCP1 pin is not affected. Only a CCP inter-
rupt is generated (if enabled).
10.2.3
SPECIAL EVENT TRIGGER
In this mode, an internal hardware trigger is generated
which may be used to initiate an action.
The special event trigger output of CCP1 resets the
TMR1 register pair. This allows the CCPR1 register to
effectively be a 16-bit programmable period register for
Timer1.
The special trigger output of CCP2 resets the TMR1
register pair, and starts an A/D conversion (if the A/D
module is enabled).
For the PIC16C72 only, the special event trigger output
of CCP1 resets the TMR1 register pair, and starts an
A/D conversion (if the A/D module is enabled).
FIGURE 10-3: COMPARE MODE
OPERATION BLOCK
DIAGRAM
Special Event
(1)
Note:
Clearing the CCP1CON register will force
the RC2/CCP1 compare output latch to the
default low level. This is not the data latch.
Note:
The special event trigger from the
CCP1and CCP2 modules will not set inter-
rupt flag bit TMR1IF (PIR1<0>).
CCPR1H CCPR1L
TMR1H
TMR1L
Comparator
Q
S
R
Output
Logic
T
Set flag bit CCP1IF
(PIR1<2>)
match
RC2/CCP1
Pin
TRISC<2>
Output Enable
CCP1CON<3:0>
Mode Select
Note 1:
For CCP1 (if enabled), reset Timer1.
For CCP2 (if enabled), reset Timer1, and set bit
GO/DONE (ADCON0<2>), which starts an A/D conver-
sion.