Real-time clock (RTC) RM0444
894/1390 RM0444 Rev 5
30.6.5 RTC prescaler register (RTC_PRER)
This register must be written in initialization mode only. The initialization must be performed
in two separate write accesses. Refer to Calendar initialization and configuration on
page 881.
This register is write protected. The write access procedure is described in RTC register
write protection on page 881.
Address offset: 0x10
Backup domain reset value: 0x007F 00FF
System reset: not affected
Bit 2 WUTWF: Wakeup timer write flag
This bit is set by hardware when WUT value can be changed, after the WUTE bit has been
set to 0 in RTC_CR.
It is cleared by hardware in initialization mode.
0: Wakeup timer configuration update not allowed except in initialization mode
1: Wakeup timer configuration update allowed
Bit 1 ALRBWF: Alarm B write flag
This bit is set by hardware when alarm B values can be changed, after the ALRBE bit has
been set to 0 in RTC_CR.
It is cleared by hardware in initialization mode.
0: Alarm B update not allowed
1: Alarm B update allowed
Bit 0 ALRAWF: Alarm A write flag
This bit is set by hardware when alarm A values can be changed, after the ALRAE bit has
been set to 0 in RTC_CR.
It is cleared by hardware in initialization mode.
0: Alarm A update not allowed
1: Alarm A update allowed
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Res. Res. Res. Res. Res. Res. Res. Res. Res. PREDIV_A[6:0]
rw rw rw rw rw rw rw
1514131211109876543210
Res. PREDIV_S[14:0]
rw rw rw rw rw rw rw rw rw rw rw rw rw rw rw
Bits 31:23 Reserved, must be kept at reset value.
Bits 22:16 PREDIV_A[6:0]: Asynchronous prescaler factor
This is the asynchronous division factor:
ck_apre frequency = RTCCLK frequency/(PREDIV_A+1)
Bit 15 Reserved, must be kept at reset value.
Bits 14:0 PREDIV_S[14:0]: Synchronous prescaler factor
This is the synchronous division factor:
ck_spre frequency = ck_apre frequency/(PREDIV_S+1)
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