PIC18F87J90 Datasheet, PDF (166/450 Pages) Microchip Technology – 64/80-Pin, High-Performance Microcontrollers with LCD Driver and nanoWatt Technology

PIC18F87J90 FAMILY
15.2.2 CLOCK SOURCE
As mentioned earlier, the RTCC module is intended to
be clocked by an external Real-Time Clock crystal,
oscillating at 32.768 kHz, but can also be an internal
oscillator. The RTCC clock selection is decided by the
RTCOSC bit (CONFIG3L<1>).
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 Section 15.2.9 “Calibration”.)
FIGURE 15-4:
CLOCK SOURCE MULTIPLEXING
32.768 kHz XTAL
from SOSC
Internal RC
1:16384
Clock Prescaler⁽¹⁾
Half Second
Clock
Half second⁽¹⁾
One Second Clock
CONFIG 3L<1>
Second
Hour:Minute
Day
Day of Week
Month
Year
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 = 0.
15.2.2.1 Real-Time Clock Enable
The RTCC module can be clocked by an external,
32.768 kHz crystal (Timer1 oscillator) or the Internal RC
oscillator, which can be selected in CONFIG3L<1>.
If the external clock is used, the Timer1 oscillator
should be enabled by setting the T1OSCEN bit
(T1CON<3> = 1). If INTRC is providing the clock, the
INTRC clock can be brought out to the RTCC pin by the
RTSECSEL<1:0> bits in the PADCFG register.
15.2.3 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
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
Table 15-1)
• Year Carry: from 99 to 00; this also surpasses the
use of the RTCC
For the day to month rollover schedule, see Table 15-2.
Considering that the following values are in BCD for-
mat, the carry to the upper BCD digit will occur at a
count of 10 and not at 16 (SECONDS, MINUTES,
HOURS, WEEKDAY, DAYS and MONTHS).
TABLE 15-1: DAY OF WEEK SCHEDULE
Day of Week
Sunday
0
Monday
1
Tuesday
2
Wednesday
3
Thursday
4
Friday
5
Saturday
6
TABLE 15-2: DAY TO MONTH ROLLOVER
SCHEDULE
Month
Maximum Day Field
01 (January)
02 (February)
31
28 or 29⁽¹⁾
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 Section 15.2.4 “Leap Year”.
DS39933D-page 166
 2010 Microchip Technology Inc.