Datasheet

PIC18F46J11 FAMILY
DS39932D-page 240  2011 Microchip Technology Inc.
17.2.2 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 also can be clocked by
the INTRC 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 17.2.9 “Calibration”.)
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 (Timer1 oscillator) or the INTRC
oscillator, which can be selected in CONFIG3L<1>.
If the Timer1 oscillator will be used as the clock source
for the RTCC, make sure to enable it by setting
T1CON<3> (T1OSCEN). The selected clock can be
brought out to the RTCC pin by the RTSECSEL<1:0>
bits in the PADCFG1 register.
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
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 17-1)
• Year Carry: From 99 to 00; this also surpasses the
use of the RTCC
For the day to month rollover schedule, see Table 17-2.
Considering that the following values are in BCD
format, 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 17-1: DAY OF WEEK SCHEDULE
Note 1: Writing to the lower half of the MINSEC register resets all counters, allowing fraction of a second synchronization;
the 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 T1OSC
Internal RC
CONFIG 3L<1>
Day of Week
Sunday 0
Monday 1
Tuesday 2
Wednesday 3
Thursday 4
Friday 5
Saturday 6