Microchip Technology AC164139 Data Sheet
PIC24FJ256DA210 FAMILY
DS39969B-page 286
2010 Microchip Technology Inc.
20.1
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
20.1.1
REGISTER MAPPING
To limit the register interface, the RTCC Timer and
Alarm Time registers are accessed through the corre-
sponding 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 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.
Alarm Time registers are accessed through the corre-
sponding 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 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
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 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.
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 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 20-2:
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, they will decrement the
ALRMPTR<1:0> value. 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, they will decrement the
ALRMPTR<1:0> value. The same applies to the
RTCVALH or RTCVALL bytes with the RTCPTR<1:0>
being decremented.
20.1.2
WRITE LOCK
In order to perform a write to any of the RTCC Timer
registers, the RTCWREN (RCFGCAL<13>) bit must be
set (refer to Example 20-1).
registers, the RTCWREN (RCFGCAL<13>) bit must be
set (refer to Example 20-1).
EXAMPLE 20-1:
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 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.
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.
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