
Real-time clock (RTC)
RM0453
1024/1454
RM0453 Rev 2
32.6.15 RTC alarm A sub second register (RTC_ALRMASSR)
This register can be written only when ALRAE is reset in RTC_CR register, or in initialization
mode.
Address offset: 0x44
Backup domain reset value: 0x0000 0000
System reset: not affected
Bit 7
MSK1
: Alarm A seconds mask
0: Alarm A set if the seconds match
1: Seconds don’t care in alarm A comparison
Bits 6:4
ST[2:0]
: Second tens in BCD format.
Bits 3:0
SU[3:0]
: Second units in BCD format.
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
SSCLR
Res.
MASKSS[5:0]
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
rw
rw
rw
rw
rw
rw
rw
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Res.
SS[14:0]
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
w
rw
rw
Bit 31
SSCLR
: Clear synchronous counter on alarm (Binary mode only)
0: The synchronous binary counter (SS[31:0] in RTC_SSR) is free-running.
1: The synchronous binary counter (SS[31:0] in RTC_SSR) is running from 0xFFFF FFFF to
RTC_ALRMABINR
→
SS[31:0] value and is automatically reloaded with 0xFFFF FFFF when
reaching RTC_ALRMABINR
→
SS[31:0].
Note: SSCLR must be kept to 0 when BCD or mixed mode is used (BIN = 00, 10 or 11).
Bit 30 Reserved, must be kept at reset value.
Bits 29:24
MASKSS[5:0]
: Mask the most-significant bits starting at this bit
0: No comparison on sub seconds for Alarm A. The alarm is set when the seconds unit is
incremented (assuming that the rest of the fields match).
1: SS[31:1] are don’t care in Alarm A comparison. Only SS[0] is compared.
2: SS[31:2] are don’t care in Alarm A comparison. Only SS[1:0] are compared.
...
31: SS[31] is don’t care in Alarm A comparison. Only SS[30:0] are compared.
From 32 to 63: All 32 SS bits are compared and must match to activate alarm.
Note: In BCD mode (BIN=00) the overflow bits of the synchronous counter (bits 31:15) are
never compared. These bits can be different from 0 only after a shift operation.
Bits 23:15 Reserved, must be kept at reset value.
Bits 14:0
SS[14:0]
:
Sub seconds value
This value is compared with the contents of the synchronous prescaler counter to determine
if alarm A is to be activated. Only bits 0 up MASKSS-1 are compared.
This field is the mirror of SS[14:0] in the RTC_ALRMABINR, and so can also be read or
written through RTC_ALRMABINR.