Microchip Technology DM183037 Data Sheet
2012 Microchip Technology Inc.
DS30575A-page 311
PIC18F97J94 FAMILY
17.2.2
CLOCK SOURCE
As mentioned earlier, the RTCC module is intended to
be clocked by an external Real-Time Clock (RTC) crys-
tal, oscillating at 32.768 kHz, but an internal oscillator
can be used. The RTCC clock selection is decided by
the RTCOSC bit (CONFIG3L<0>).
be clocked by an external Real-Time Clock (RTC) crys-
tal, oscillating at 32.768 kHz, but an internal oscillator
can be used. The RTCC clock selection is decided by
the RTCOSC bit (CONFIG3L<0>).
Calibration of the crystal can be done through this
module to yield an error of 3 seconds or less per month.
(For further details, see
module to yield an error of 3 seconds or less per month.
(For further details, see
.)
FIGURE 17-4:
CLOCK SOURCE MULTIPLEXING
17.2.2.1
Real-Time Clock Enable
The RTCC module can be clocked by an external,
32.768 kHz crystal (SOSC Oscillator) or the LF-INTOSC
Oscillator, which can be selected in CONFIG3L<0>.
If the external clock is used, the SOSC Oscillator
should be enabled. If LF-INTOSC is providing the clock,
the INTOSC clock can be brought out to the RTCC pin
by the RTSECSEL<1:0> bits (RTCCON2<1:0>).
32.768 kHz crystal (SOSC Oscillator) or the LF-INTOSC
Oscillator, which can be selected in CONFIG3L<0>.
If the external clock is used, the SOSC Oscillator
should be enabled. If LF-INTOSC is providing the clock,
the INTOSC clock can be brought out to the RTCC pin
by the RTSECSEL<1:0> bits (RTCCON2<1:0>).
17.2.3
DIGIT CARRY RULES
This section explains which timer values are affected
when there is a rollover:
• Time of Day: From 23:59:59 to 00:00:00 with a
when there is a rollover:
• Time of Day: From 23:59:59 to 00:00:00 with a
carry to the Day field
• Month: From 12/31 to 01/01 with a carry to the
Year field
• Day of Week: From 6 to 0 with no carry (see
)
• Year Carry: From 99 to 00; this also surpasses the
use of the RTCC
For the day-to-month rollover schedule, see
Because the following values are in BCD format, the
carry to the upper BCD digit occurs at the count of 10,
not 16 (SECONDS, MINUTES, HOURS, WEEKDAY,
DAYS and MONTHS).
carry to the upper BCD digit occurs at the count of 10,
not 16 (SECONDS, MINUTES, HOURS, WEEKDAY,
DAYS and MONTHS).
TABLE 17-1:
DAY OF WEEK SCHEDULE
TABLE 17-2:
DAY TO MONTH ROLLOVER
SCHEDULE
SCHEDULE
Note 1:
Writing to the lower half of the MINSEC register resets all counters, allowing fraction of a second synchronization;
clock prescaler is held in Reset when RTCEN =
clock prescaler is held in Reset when RTCEN =
0
.
32.768 kHz XTAL
1:16384
Half Second
(1)
Half-Second
Clock
One Second Clock
Year
Month
Day
Day of Week
Second
Hour:Minute
Clock Prescaler
(1)
from SOSC
Internal RC
RTCCON1
Day of Week
Sunday
0
Monday
1
Tuesday
2
Wednesday
3
Thursday
4
Friday
5
Saturday
6
Month
Maximum Day Field
01 (January)
31
02 (February)
28 or 29
03 (March)
31
04 (April)
30
05 (May)
31
06 (June)
30
07 (July)
31
08 (August)
31
09 (September)
30
10 (October)
31
11 (November)
30
12 (December)
31
Note 1: See
.