RM0090 Real-time clock (RTC)
Doc ID 018909 Rev 4 650/1422
23.6.7 RTC calibration register (RTC_CALIBR)
Address offset: 0x18
Power-on reset value: 0x0000 0000
System reset: not affected
Note: This register can be written in initialization mode only (RTC_ISR/INITF = ‘1’).
This register is write protected. The write access procedure is described in RTC register
write protection on page 630.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Reserved
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Reserved
DCS
Reserved
DC[4:0]
rw rw rw rw rw rw
Bits 31:8 Reserved
Bit 7 DCS: Digital calibration sign
0: Positive calibration: calendar update frequency is increased
1: Negative calibration: calendar update frequency is decreased
Bits 6:5 Reserved, must be kept at reset value.
Bits 4:0 DC[4:0]: Digital calibration
DCS = 0 (positive calibration)
00000: + 0 ppm
00001: + 4 ppm (rounded value)
00010: + 8 ppm (rounded value)
..
11111: + 126 ppm (rounded value)
DCS = 1 (negative calibration)
00000: −0 ppm
00001: −2 ppm (rounded value)
00010: −4 ppm (rounded value)
..
11111: −63 ppm (rounded value)
Refer to Case of RTCCLK=32.768 kHz and PREDIV_A+1=128 on page 635 for the exact
step value.
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