PIC24FJ256GB108-I Datasheet, PDF (252/352 Pages) Microchip Technology – 64/80/100-Pin, 16-Bit Flash Microcontrollers with USB On-The-Go (OTG)

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20.1 RTCC Module Registers
The RTCC module registers are organized into three
categories:
• RTCC Control Registers
• RTCC Value Registers
• Alarm Value Registers
20.1.1 REGISTER MAPPING
To limit the register interface, the RTCC Timer and
Alarm Time registers are accessed through
corresponding register pointers. The RTCC Value reg-
ister window (RTCVALH and RTCVALL) uses the
RTCPTR bits (RCFGCAL<9:8>) to select the desired
Timer register pair (see Table 20-1).
By writing the RTCVALH byte, the RTCC Pointer value,
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 20-1: RTCVAL REGISTER MAPPING
RTCPTR
<1:0>
RTCC Value Register Window
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 20-2).
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.
EXAMPLE 20-1: SETTING THE RTCWREN BIT
__builtin_write_RTCWEN(); //set the RTCWREN bit
TABLE 20-2: 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 will decrement the ALRMPTR<1:0>
value. 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.
20.1.2 WRITE LOCK
In order to perform a write to any of the RTCC Timer
registers, the RTCWREN bit (RCFGCAL<13>) must be
set (refer to Example 20-1).
Note:
To avoid accidental writes to the timer, it is
recommended that the RTCWREN bit
(RCFGCAL<13>) is kept clear at any
other time. For the RTCWREN bit to be
set, there is only 1 instruction cycle time
window allowed between the unlock
sequence and the setting of RTCWREN;
therefore, it is recommended that code
follow the procedure in Example 20-1.
For applications written in C, the unlock
sequence should be implemented using
in-line assembly.
DS39897C-page 252
 2009 Microchip Technology Inc.