PIC18FXX20
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 up to 200 kHz. See Section 12.0
for further details.
If the CCP module is configured in Compare mode
to
generate
a
“special
event
trigger”
(CCP1M3:CCP1M0 = 1011), this signal will reset
Timer3.
Note: The special event triggers from the CCP
module will not set interrupt flag bit,
TMR3IF (PIR1<0>).
14.3 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/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 registers 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
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
POR, BOR
GIE/
GIEH
PEIE/
GIEL
INTCON
TMR0IE
INT0IE
RBIE
TMR0IF
INT0IF
RBIF
0000 0000 0000 0000
PIR2
PIE2
IPR2
TMR3L
TMR3H
T1CON
T3CON
—
—
—
—
—
—
—
—
—
EEIF
EEIE
EEIP
BCLIF
BCLIE
BCLIP
LVDIF
LVDIE
LVDIP
TMR3IF
TMR3IE
TMR3IP
CCP2IF ---0 0000 ---0 0000
CCP2IE ---0 0000 ---0 0000
CCP2IP ---1 1111 ---1 1111
xxxx xxxx uuuu uuuu
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
RD16
RD16
xxxx xxxx uuuu uuuu
—
T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON 0-00 0000 u-uu 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.
Advance Information
DS39609A-page 145
MICROCHIP [ MICROCHIP ]
