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2002 Microchip Technology Inc.
Preliminary
DS40044A-page 51
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 con-
tinue to run during SLEEP. It is primarily intended for a
32.768 kHz watch crystal. Table 7-1 shows the capaci-
tor 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” (CCP1M3:CCP1M0
=
1011
), this signal will RESET Timer1.
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 CCPRxH:CCPRxL regis-
ters 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.
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
These values are for design guidance only.
Consult AN826 (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.