ST STM32F405 User Manual

RM0090 Rev 18 813/1749
RM0090 Real-time clock (RTC)
838
samples are observed at the level designated by the TAMPxTRG bits
(TAMP1TRG/TAMP2TRG).
The TAMPER inputs are pre-charged through the I/O internal pull-up resistance before its
state is sampled, unless disabled by setting TAMPPUDIS to 1,The duration of the precharge
is determined by the TAMPPRCH bits, allowing for larger capacitances on the tamper
inputs.
The trade-off between tamper detection latency and power consumption through the pull-up
can be optimized by using TAMPFREQ to determine the frequency of the sampling for level
detection.
Note: Refer to the datasheets for the electrical characteristics of the pull-up resistors.
TAMPER alternate function detection
The TAMPER1 alternate function (RTC_TAMP1) can be mapped either to RTC_AF1(PC13)
or RTC_AF2 (PI8) depending on the value of TAMP1INSEL bit in RTC_TAFCR register (see
Section 26.6.17: RTC tamper and alternate function configuration register (RTC_TAFCR)).
TAMPE bit must be cleared when TAMP1INSEL is modified to avoid unwanted setting of
TAMPF.
The TAMPER 2 alternate function corresponds to RTC_TAMP2 pin.
26.3.14 Calibration clock output
When the COE bit is set to 1 in the RTC_CR register, a reference clock is provided on the
RTC_CALIB device output. If the COSEL bit in the RTC_CR register is reset and
PREDIV_A = 0x7F, the RTC_CALIB frequency is f
RTCCLK
/64
. This corresponds to a
calibration output at 512 Hz for an RTCCLK frequency at 32.768 kHz.
The RTC_CALIB output is not impacted by the calibration value programmed in
RTC_CALIBR register. The RTC_CALIB duty cycle is irregular: there is a light jitter on falling
edges. It is therefore recommended to use rising edges.
If COSEL is set and (PREDIV_S+1) is a non-zero multiple of 256 (i.e: PREDIV_S[7:0] =
0xFF), the RTC_CALIB frequency is f
RTCCLK/(256 * (PREDIV_A+1)). This corresponds to a
calibration output at 1 Hz for prescaler default values (PREDIV_A = 0x7F, PREDIV_S =
0xFF), with an RTCCLK frequency at 32.768 kHz. The 1 Hz output is affected when a shift
operation is on going and may toggle during the shift operation (SHPF=1).
Calibration alternate function output
When the COE bit in the RTC_CR register is set to 1, the calibration alternate function
(RTC_CALIB) is enabled on RTC_AF1.
Note: When RTC_CALIB or RTC_ALARM is selected, RTC_AF1 is automatically configured in
output alternate function.
26.3.15 Alarm output
Three functions can be selected on Alarm output: ALRAF, ALRBF and WUTF. These
functions reflect the contents of the corresponding flags in the RTC_ISR register.
The OSEL[1:0] control bits in the RTC_CR register are used to activate the alarm alternate
function output (RTC_ALARM) in RTC_AF1, and to select the function which is output on
RTC_ALARM.

ST STM32F405 Specifications

General

Brand	ST
Model	STM32F405
Category	Computer Hardware
Language	English