Production Data
WM8352
22 REAL-TIME CLOCK (RTC)
22.1 GENERAL DESCRIPTION
The WM8352 contains a Real Time Clock (RTC), which maintains the current date and time, and
also has the capability to generate alarms and periodic interrupt signals. The RTC is powered by the
backup supply (VRTC), in order that it can keep running when the normal power sources are
unavailable.
The RTC uses the 32.768kHz clock generated by the on-chip crystal oscillator. To compensate for
errors in this clock frequency, the RTC includes a frequency trim option. Alternatively the RTC can be
clocked from external 32.768kHz input on a GPIO pin configured as 32kHz input. See Section 12.2
for details of the 32kHz oscillator control.
22.2 RTC CONTROL
22.2.1 MODES OF OPERATION
The Real Time Clock is enabled when RTC_TICK_ENA is set to 1. (This is the default setting.) See
Table 135 for the definition of this RTC_TICK_ENA.
The RTC can operate as a 24-hour clock or else as a 12-hour clock with a separate AM/PM flag bit.
The RTC time register fields can be treated as BCD (binary-coded decimal) or as binary data
formats. These options are selected as described in Table 130.
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R23 (17h)
15
RTC_BCD
0
RTC Coding (applies to all time
registers)
RTC Time
control
0 = Binary
1 = BCD
14
RTC_12HR
0
RTC 12/24 hours mode
1 = 12 hours (MSB of RTC_HRS
indicates AM/PM)
0 = 24 hours (MSB of RTC_HRS is 0)
Table 130 RTC Modes of Operation
22.2.2 RTC TIME REGISTERS
The current time and date are held in registers R16 to R19, as described in Table 131.
ADDRESS
R16 (10h)
BIT
14:8
6:0
LABEL
DEFAULT
000 0000
000 0000
1
DESCRIPTION
RTC Minutes; 0 to 59
RTC_MINS [6:0]
RTC_SECS [6:0]
RTC_DAY [2:0]
RTC sec / min
R17 (11h)
RTC Seconds; 0 to 59
10:8
RTC Day of the week; 1 to 7, 1 =
Sunday
RTC hour / day
5
RTC_HPM
0
RTC Hours AM/PM flag
0 = AM
1 = PM
Only valid in 12hour mode.
4:0
RTC_HRS [4:0]
0 0000
Hours register with 0-23 range in
24hour mode and 1-12 in 12 hour
mode.
R18 (12h)
RTC date
R19 (13h)
RTC year
12:8
5:0
RTC_MTH [5:0]
RTC_DATE [5:0]
0_0001
00_0001
01_0100
Month register with range 1-12.
Date register with range 1-31.
13:8
RTC_YHUNDRED
S [6:0]
Year hundreds register tied to
20(dec)
7:0
RTC_YUNITS
[7:0]
0000_0000
Year units register with range 0-99.
Table 131 RTC Time Registers
PD, February 2011, Rev 4.4
189
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
