PIC18F44J50-I Datasheet, PDF (238/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

PIC18F46J50 FAMILY
17.2.2 CLOCK SOURCE
As mentioned earlier, the RTCC module is intended to
be clocked by an external Real-Time Clock (RTC) crystal
oscillating at 32.768 kHz, but can also be clocked by the
INTRC. 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
32.768 kHz XTAL
from T1OSC
Internal RC
CONFIG 3L<1>
1:16384
Clock Prescaler⁽¹⁾
Half-Second
Clock
Half Second⁽¹⁾
One-Second Clock
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.
17.2.2.1 Real-Time Clock Enable
The RTCC module can be clocked by an external,
32.768 kHz crystal (Timer1 oscillator or T1CKI input) 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 RTC clock can
be brought out to the RTCC pin by the
RTSECSEL<1:0> bits in the PADCFG 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
Day of Week
Sunday
0
Monday
1
Tuesday
2
Wednesday
3
Thursday
4
Friday
5
Saturday
6
DS39931D-page 238
 2011 Microchip Technology Inc.