
M451
May. 4, 2018
Page
558
of
1006
Rev.2.08
M4
51
S
E
RI
E
S
T
E
CH
NICA
L RE
F
E
R
E
NC
E
M
A
NU
A
L
6.12.3 Block Diagram
The RTC block diagram is shown below.
RTC Time Counter
Control Unit
Time Loading
Register
(RTC_TIME)
Calendar
Loading
Register
(RTC_CAL)
Time Alarm
Register
(RTC_TALM)
Calendar
Alarm Register
(RTC_CALM)
1/128 change
1/64 change
1/32 change
1/16 change
1/8 change
1/4 change
1/2 change
1 change
(sec)
111
110
101
100
011
010
001
000
TICK (RTC_TICK[2:0])
TICKIF (RTC_INTSTS[1])
TICKIEN (RTC_INTEN[1])
Compare
Operation
ALMIEN (RTC_INTEN[0])
Alarm Interrupt
RTC_CLK
Frequency
Compensation
Frequency
Compensation
Register
(RTC_FREQADJ)
RWEN
WEEKDAY
LEAPYEAR
24H/12H
ALMIF (RTC_INTSTS[0])
Wakeup CPU from
Power-down mode
Tick Interrupt
Time Alarm
Mask Register
(RTC_TAMSK)
Calendar Alarm
Mask Register
(RTC_CAMSK)
Snoop Interrupt
SNPDIEN (RTC_INTEN[2])
Snoop Detection Logic
80 Bytes Spare Registers
(RTC_SPR0 ~ RTC_SPR19)
LIRC
0
1
RTCSEL
(CLK_CLKSEL3[8])
LXT
TAMPER
V
BAT
SNPDIF (RTC_INTSTS[2])
INIT
INIT
RWEN
LEAPYEAR
CLKFMT
WEEKDAY
SPRCTL
Figure 6.12-1 RTC Block Diagram
6.12.4 Basic Configuration
The RTC controller clock source is enabled by RTCCKEN (APBCLK[1]) and low speed 32 kHz
oscillator is enabled by LXTEN (CLK_PWRCTL[1]).
6.12.5 Functional Description
RTC Initiation
6.12.5.1
When a RTC block is powered on, RTC is at reset state. User has to write a number 0xa5eb1357
to RTC initial register RTC_INIT (INIT[31:0]) to make RTC leaving reset state. Once the
RTC_INIT register is written as 0xa5eb1357, the RTC will be in normal active state permanently.
User can read Active bit (INIT[0]) to check the RTC is at normal active state or reset state.
Access to RTC register
6.12.5.2
Due to clock frequency difference between RTC clock and system clock, when user writes new
data to any one of the RTC registers, the data will not be updated until 2 RTC clocks later (about
60us).
In addition, user must be aware that RTC controller does not check whether loaded data is out of
bounds or not in RTC_TIME, RTC_CAL, RTC_TALM and RTC_CALM registers. RTC does not