PIC18F2220/2320/4220/4320
14.2 Timer1 Oscillator
14.4 Resetting Timer3 Using a CCP
Trigger Output
The Timer1 oscillator may be used as the clock source
for Timer3. The Timer1 oscillator is enabled by setting
the T1OSCEN (T1CON<3>) bit. The oscillator is a low-
power oscillator rated for 32 kHz crystals. See
Section 12.2 “Timer1 Oscillator” for further details.
If the CCP module is configured in Compare mode
to generate “special event trigger”
a
(CCP1M3:CCP1M0 = 1011), this signal will reset
Timer3. See Section 15.4.4 “Special Event Trigger”
for more information.
14.3 Timer3 Interrupt
Note:
The special event triggers from the CCP
module will not set interrupt flag bit,
TMR3IF (PIR1<0>).
The TMR3 register pair (TMR3H:TMR3L) increments
from 0000h to FFFFh and rolls over to 0000h. The
TMR3 interrupt, if enabled, is generated on overflow
which is latched in interrupt flag bit, TMR3IF
(PIR2<1>). This interrupt can be enabled/disabled by
setting/clearing TMR3 Interrupt Enable bit, TMR3IE
(PIE2<1>).
Timer3 must be configured for either Timer or Synchro-
nized Counter mode to take advantage of this feature.
If Timer3 is running in Asynchronous Counter mode,
this Reset operation may not work. In the event that a
write to Timer3 coincides with a special event trigger
from CCP1, the write will take precedence. In this mode
of operation, the CCPR1H:CCPR1L register pair
effectively becomes the period register for Timer3.
TABLE 14-1: REGISTERS ASSOCIATED WITH TIMER3 AS A TIMER/COUNTER
Value on
all other
Resets
Value on
POR, BOR
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
INTCON
GIE/
GIEH
PEIE/
GIEL
TMR0IE
INT0IE
RBIE
TMR0IF
INT0IF
RBIF
0000 000x 0000 000u
PIR2
OSCIF
OSCIE
OSCIP
CMIF
CMIE
CMIP
—
—
—
EEIF
EEIE
EEIP
BCLIF
BCLIE
BCLIP
LVDIF
LVDIE
LVDIP
TMR3IF
TMR3IE
TMR3IP
CCP2IF 00-0 0000 00-0 0000
CCP2IE 00-0 0000 00-0 0000
CCP2IP 11-1 1111 11-1 1111
xxxx xxxx uuuu uuuu
PIE2
IPR2
TMR3L
TMR3H
T1CON
T3CON
Holding Register for the Least Significant Byte of the 16-bit TMR3 Register
Holding Register for the Most Significant Byte of the 16-bit TMR3 Register
xxxx xxxx uuuu uuuu
RD16
RD16
T1RUN T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON 0000 0000 u0uu uuuu
T3CCP2 T3CKPS1 T3CKPS0 T3CCP1 T3SYNC TMR3CS TMR3ON 0000 0000 uuuu uuuu
Legend: x= unknown, u= unchanged, -= unimplemented, read as ‘0’. Shaded cells are not used by the Timer3 module.
2003 Microchip Technology Inc.
DS39599C-page 131
MICROCHIP [ MICROCHIP ]
