Datasheet
PIC16C77X
1999-2013 Microchip Technology Inc. Advance Information DS30275B-page 43
5.2 Timer1 Oscillator
A crystal oscillator circuit is built in between pins T1OSI
(input) and T1OSO (amplifier output). It is enabled by
setting control bit T1OSCEN (T1CON<3>). The oscilla-
tor is a low power oscillator rated up to 200 kHz. It will
continue to run during SLEEP. It is primarily intended
for a 32 kHz crystal. Ta bl e 5 - 1 shows the capacitor
selection for the Timer1 oscillator.
The Timer1 oscillator is identical to the LP oscillator.
The user must provide a software time delay to ensure
proper oscillator start-up.
TABLE 5-1 CAPACITOR SELECTION FOR
THE TIMER1 OSCILLATOR
5.3 Timer1 Interrupt
The TMR1 Register pair (TMR1H:TMR1L) increments
from 0000h to FFFFh and rolls over to 0000h. The
TMR1 Interrupt, if enabled, is generated on overflow
which is latched in interrupt flag bit TMR1IF (PIR1<0>).
This interrupt can be enabled/disabled by setting/clear-
ing TMR1 interrupt enable bit TMR1IE (PIE1<0>).
5.4 Resetting Timer1 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 Timer1 and start an A/D
conversion (if the A/D module is enabled).
Timer1 must be configured for either timer or synchro-
nized counter mode to take advantage of this feature. If
Timer1 is running in asynchronous counter mode, this
reset operation may not work.
In the event that a write to Timer1 coincides with a spe-
cial event trigger from CCP1, the write will take prece-
dence.
In this mode of operation, the CCPR1H:CCPR1L regis-
ters pair effectively becomes the period register for
Timer1.
TABLE 5-2 REGISTERS ASSOCIATED WITH TIMER1 AS A TIMER/COUNTER
Osc Type Freq C1 C2
LP 32 kHz 33 pF 33 pF
100 kHz 15 pF 15 pF
200 kHz 15 pF 15 pF
These values are for design guidance only.
Crystals Tested:
32.768 kHz Epson C-001R32.768K-A 20 PPM
100 kHz Epson C-2 100.00 KC-P 20 PPM
200 kHz STD XTL 200.000 kHz 20 PPM
Note 1: Higher capacitance increases the stability
of oscillator but also increases the start-up
time.
2: Since each resonator/crystal has its own
characteristics, the user should consult the
resonator/crystal manufacturer for appropri-
ate values of external components.
Note: The special event triggers from the CCP1
module will not set interrupt flag bit
TMR1IF (PIR1<0>).
Address 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
0Bh,8Bh,
10Bh,18Bh
INTCON GIE PEIE
T0IE INTE RBIE T0IF INTF RBIF
0000 000x 0000 000u
0Ch PIR1
PSPIF
(1)
ADIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF
0000 0000 0000 0000
8Ch PIE1 PSPIE
(1)
ADIE RCIE TXIE SSPIE CCP1IE TMR2IE TMR1IE
0000 0000 0000 0000
0Eh TMR1L Holding register for the Least Significant Byte of the 16-bit TMR1 register
xxxx xxxx uuuu uuuu
0Fh TMR1H Holding register for the Most Significant Byte of the 16-bit TMR1 register
xxxx xxxx uuuu uuuu
10h T1CON
— — T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON
--00 0000 --uu uuuu
Legend: x = unknown, u = unchanged, - = unimplemented read as '0'. Shaded cells are not used by the Timer1 module.
Note 1: These bits are reserved on the 28-pin devices, always maintain these bits clear.
774.book Page 43 Tuesday, January 29, 2013 12:02 PM