Datasheet

© 2009 Microchip Technology Inc. DS40044G-page 53
PIC16F627A/628A/648A
7.4 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>). It will
continue to run during Sleep. It is primarily intended for
a 32.768 kHz watch crystal. Table 7-1 shows the
capacitor selection for the Timer1 oscillator.
The user must provide a software time delay to ensure
proper oscillator start-up.
TABLE 7-1: CAPACITOR SELECTION FOR
THE TIMER1 OSCILLATOR
7.5 Resetting Timer1 Using a CCP
Trigger Output
If the CCP1 module is configured in Compare mode to
generate a “special event trigger” (CCP1M<3:0> =
1011), this signal will reset Timer1.
Timer1 must be configured for either timer or
Synchronized 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
special event trigger from CCP1, the write will take
precedence.
In this mode of operation, the CCPRxH:CCPRxL
register pair effectively becomes the period register for
Timer1.
7.6 Resetting Timer1 Register Pair
(TMR1H, TMR1L)
TMR1H and TMR1L registers are not reset to 00h on
a POR or any other Reset except by the CCP1 special
event triggers (see Section 9.2.4 “Special Event
Trigger”).
T1CON register is reset to 00h on a Power-on Reset or
a Brown-out Reset, which shuts off the timer and
leaves a 1:1 prescale. In all other Resets, the register
is unaffected.
7.7 Timer1 Prescaler
The prescaler counter is cleared on writes to the
TMR1H or TMR1L registers.
TABLE 7-2: REGISTERS ASSOCIATED WITH TIMER1 AS A TIMER/COUNTER
Freq C1 C2
32.768 kHz 15 pF 15 pF
Note: These values are for design guidance only.
Consult Application Note AN826 “Crystal
Oscillator Basics and Crystal Selection for
rfPIC
®
and PIC
®
Devices” (DS00826) for
further information on Crystal/Capacitor
Selection.
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
Value on
all other
Resets
0Bh, 8Bh,
10Bh, 18Bh
INTCON GIE PEIE
T0IE INTE RBIE T0IF INTF RBIF 0000 000x 0000 000u
0Ch PIR1
EEIF CMIF RCIF TXIF — CCP1IF TMR2IF TMR1IF 0000 -000 0000 -000
8Ch PIE1
EEIE CMIE RCIE TXIE — CCP1IE TMR2IE TMR1IE 0000 -000 0000 -000
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.