Microchip Technology MA240017 Data Sheet
PIC24F16KA102 FAMILY
DS39927C-page 156
2008-2011 Microchip Technology Inc.
19.2
RTCC Module Registers
The RTCC module registers are organized into three
categories:
• RTCC Control Registers
• RTCC Value Registers
• Alarm Value Registers
categories:
• RTCC Control Registers
• RTCC Value Registers
• Alarm Value Registers
19.2.1
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
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
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.
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 19-1:
RTCVAL REGISTER MAPPING
The Alarm Value register window (ALRMVALH
and ALRMVALL) uses the ALRMPTR bits
(ALCFGRPT<9:8>) to select the desired Alarm register
pair (see
and ALRMVALL) uses the ALRMPTR bits
(ALCFGRPT<9:8>) to select the desired Alarm register
pair (see
).
By writing the ALRMVALH byte, the Alarm Pointer
value bits (ALRMPTR<1:0>) 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.
value bits (ALRMPTR<1:0>) 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 19-2:
ALRMVAL REGISTER
MAPPING
MAPPING
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.
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.
19.2.2
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
registers, the RTCWREN bit (RCFGCAL<13>) must be
set (refer to
).
19.2.3
SELECTING RTCC CLOCK SOURCE
The clock source for the RTCC module can be selected
using the RTCOSC (FDS<5>) bit. When the bit is set to
‘1’, the Secondary Oscillator (SOSC) is used as the ref-
erence clock and when the bit is ‘0’, LPRC is used as
the reference clock.
using the RTCOSC (FDS<5>) bit. When the bit is set to
‘1’, the Secondary Oscillator (SOSC) is used as the ref-
erence clock and when the bit is ‘0’, LPRC is used as
the reference clock.
EXAMPLE 19-1:
SETTING THE RTCWREN BIT
RTCPTR<1:0>
RTCC Value Register Window
RTCVAL<15:8>
RTCVAL<7:0>
00
MINUTES
SECONDS
01
WEEKDAY
HOURS
10
MONTH
DAY
11
—
YEAR
ALRMPTR
<1:0>
Alarm Value Register Window
ALRMVAL<15:8> ALRMVAL<7:0>
00
ALRMMIN
ALRMSEC
01
ALRMWD
ALRMHR
10
ALRMMNTH
ALRMDAY
11
—
—
Note:
This only applies to read operations and
not write operations.
not write operations.
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 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
recommended that the RTCWREN bit
(RCFGCAL<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
.
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 _RCFGCAL, #13
"
)
; //set the RTCWREN bit
asm volatile ("pop w8
"
) ;
asm volatile (
"
pop w7
"
);