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PIC18F45J50-I/SOSQTP

28/44-Pin, Low-Power, High-Performance USB Microcontrollers with nanoWatt XLP Technology

Microchip Technology 

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.

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