PIC24FJ128GA310-I Datasheet, PDF (276/406 Pages) Microchip Technology – 64/80/100-Pin, General Purpose, 16-Bit Flash Microcontrollers with LCD Controller and nanoWatt XLP Technology

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22.2 RTCC Module Registers
The RTCC module registers are organized into three
categories:
• RTCC Control Registers
• RTCC Value Registers
• Alarm Value Registers
22.2.1 REGISTER MAPPING
To limit the register interface, the RTCC Timer and
Alarm Time registers are accessed through
corresponding register pointers. The RTCC Value
register window (RTCVALH and RTCVALL) uses the
RTCPTR bits (RCFGCAL<9:8>) to select the desired
Timer register pair (see Table 22-1).
By writing the RTCVALH byte, the RTCC Pointer value,
the RTCPTR<1:0> bits decrement by one until they
reach ‘00’. Once they reach ‘00’, the MINUTES and
SECONDS value will be accessible through RTCVALH
and RTCVALL until the pointer value is manually
changed.
TABLE 22-1: RTCVAL REGISTER MAPPING
RTCC Value Register Window
RTCPTR<1:0>
RTCVAL<15:8> RTCVAL<7:0>
00
MINUTES
SECONDS
01
WEEKDAY
HOURS
10
MONTH
DAY
11
—
YEAR
The Alarm Value register window (ALRMVALH and
ALRMVALL) uses the ALRMPTR bits
(ALCFGRPT<9:8>) to select the desired Alarm register
pair (see Table 22-2).
By writing the ALRMVALH byte, the Alarm Pointer
value, ALRMPTR<1:0> bits, decrement by one until
they reach ‘00’. Once they reach ‘00’, the ALRMMIN
and ALRMSEC value will be accessible through
ALRMVALH and ALRMVALL until the pointer value is
manually changed.
TABLE 22-2: ALRMVAL REGISTER
MAPPING
ALRMPTR
Alarm Value Register Window
<1:0>
ALRMVAL<15:8> ALRMVAL<7:0>
00
ALRMMIN
ALRMSEC
01
ALRMWD
ALRMHR
10
ALRMMNTH
ALRMDAY
11
—
—
Considering that the 16-bit core does not distinguish
between 8-bit and 16-bit read operations, the user must
be aware that when reading either the ALRMVALH or
ALRMVALL bytes, the ALRMPTR<1:0> value will be
decremented. The same applies to the RTCVALH or
RTCVALL bytes with the RTCPTR<1:0> being
decremented.
Note: This only applies to read operations and
not write operations.
22.2.2 WRITE LOCK
In order to perform a write to any of the RTCC Timer
registers, the RTCWREN bit (RCFGCAL1<13>) must
be set (see Example 22-1).
Note:
To avoid accidental writes to the timer, it is
recommended that the RTCWREN bit
(RCFGCAL1<13>) is kept clear at any
other time. For the RTCWREN bit to be
set, there is only one instruction cycle time
window allowed between the 55h/AA
sequence and the setting of RTCWREN;
therefore, it is recommended that code
follow the procedure in Example 22-1.
22.2.3 SELECTING RTCC CLOCK SOURCE
The clock source for the RTCC module can be selected
using the RTCLK<1:0> bits in the RTCPWC register.
When the bits are set to ‘00’, the Secondary Oscillator
(SOSC) is used as the reference clock and when the bits
are ‘01’, LPRC is used as the reference clock. When
RTCLK<1:0> = 10 and 11, the external power line
(50 Hz and 60 Hz) is used as the clock source.
EXAMPLE 22-1: SETTING THE RTCWREN BIT
asm volatile(“push w7”);
asm volatile(“push w8”);
asm volatile(“disi #5”);
asm volatile(“mov #0x55, w7”);
asm volatile(“mov w7, _NVMKEY”);
asm volatile(“mov #0xAA, w8”);
asm volatile(“mov w8, _NVMKEY”);
asm volatile(“bset _RCFGCAL1, #13”); //set the RTCWREN bit
asm volatile(“pop w8”);
asm volatile(“pop w7”);
DS39996F-page 276
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