
2001 Microchip Technology Inc.
DS39206C-page 105
PIC18CXX2
12.2
Timer1 Oscillator
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
for further details.
12.3
Timer3 Interrupt
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/clear-
ing TMR3 interrupt enable bit, TMR3IE (PIE2<1>).
12.4
Resetting Timer3 Using a CCP
Trigger Output
If the CCP module is configured in Compare mode to
generate a “special event trigger” (CCP1M3:CCP1M0
= 1011), this signal will reset Timer3.
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 registers pair
effectively becomes the period register for Timer3.
TABLE 12-1:
REGISTERS ASSOCIATED WITH TIMER3 AS A TIMER/COUNTER
Note:
The special event triggers from the CCP
module will not set interrupt flag bit
TMR3IF (PIR1<0>).
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
POR,
BOR
Value on
all other
RESETS
INTCON
GIE/
GIEH
PEIE/
GIEL
TMR0IE
INT0IE
RBIE
TMR0IF
INT0IF
RBIF
0000 000x
0000 000u
PIR2
—
BCLIF
LVDIF
TMR3IF
CCP2IF
0000 0000
PIE2
—
BCLIE
LVDIE
TMR3IE
CCP2IE
0000 0000
IPR2
—
BCLIP
LVDIP
TMR3IP
CCP2IP
0000 0000
TMR3L
Holding Register for the Least Significant Byte of the 16-bit TMR3 Register
xxxx xxxx
uuuu uuuu
TMR3H
Holding Register for the Most Significant Byte of the 16-bit TMR3 Register
xxxx xxxx
uuuu uuuu
T1CON
RD16
—
T1CKPS1 T1CKPS0 T1OSCEN
T1SYNC
TMR1CS
TMR1ON --00 0000
--uu uuuu
T3CON
RD16
T3CCP2
T3CKPS1 T3CKPS0
T3CCP1
T3SYNC
TMR3CS
TMR3ON
-000 0000
-uuu uuuu
Legend:
x
= unknown, u = unchanged, - = unimplemented, read as '0'. Shaded cells are not used by the Timer1 module.