wm8351 Wolfson Microelectronics plc, wm8351 Datasheet - Page 189

• Manufacturer Part Number: wm8351
• Description: Wolfson Audioplus? Stereo Codec With Power Management
• Manufacturer: Wolfson Microelectronics plc

Production Data
22 REAL-TIME CLOCK (RTC)
22.1 GENERAL DESCRIPTION
22.2 RTC CONTROL
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The WM8351 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.
22.2.1
The Real Time Clock is enabled when RTC_TICK_ENA is set to 1. (This is the default setting.) See
Table 134 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 129.
R23 (17h)
RTC Time
control
Table 129 RTC Modes of Operation
22.2.2
The current time and date are held in registers R16 to R19, as described in Table 130.
R16 (10h)
RTC sec / min
R17 (11h)
RTC hour / day
R18 (12h)
RTC date
R19 (13h)
RTC year
Table 130 RTC Time Registers
ADDRESS
ADDRESS
MODES OF OPERATION
RTC TIME REGISTERS
BIT
15
14
14:8
10:8
12:8
13:8
BIT
6:0
4:0
5:0
7:0
5
RTC_BCD
RTC_12HR
RTC_MINS [6:0]
RTC_SECS [6:0]
RTC_DAY [2:0]
RTC_HPM
RTC_HRS [4:0]
RTC_MTH [5:0]
RTC_DATE [5:0]
RTC_YHUNDRED
S [6:0]
RTC_YUNITS
[7:0]
LABEL
LABEL
DEFAULT
0
0
0000_0000
DEFAULT
000 0000
000 0000
00_0001
01_0100
0_0001
0 0000
1
0
RTC Coding (applies to all time
registers)
0 = Binary
1 = BCD
RTC 12/24 hours mode
1 = 12 hours (MSB of RTC_HRS
indicates AM/PM)
0 = 24 hours (MSB of RTC_HRS is 0)
Minutes; 0 to 59
Seconds; 0 to 59
Day of the week; 1 to 7, 1 =
Sunday
RTC Hours AM/PM flag
0 = AM
1 = PM
Only valid in 12hour mode.
Hours register with 0-23 range in
24hour mode and 1-12 in 12 hour
mode.
Month register with range 1-12.
Date register with range 1-31.
Year hundreds register tied to
20(dec)
Year units register with range 0-99.
DESCRIPTION
DESCRIPTION
PD, June 2009, Rev 4.1
WM8351
189