Calibration Clock Output - ST STM32F205 series Reference Manual

Real-time clock (RTC)
Edge detection on tamper inputs
TAMPER pins generate tamper detection events when either a rising edge is observed or
an falling edge is observed depending on the corresponding TAMPxTRG bit. The internal
pull-up resistors on the TAMPER inputs are deactivated when edge detection is selected.
Caution: To avoid losing tamper detection events, the signal used for edge detection is logically
ANDed with TAMPxE in order to detect a tamper detection event in case it occurs before the
TAMPERx pin is enabled.
•
When TAMPxTRG = 0: if the TAMPERx alternate function is already high before
tamper detection is enabled (TAMPxE bit set to 1), a tamper event is detected as soon
as TAMPERx is enabled, even if there was no rising edge on TAMPERx after TAMPxE
was set.
•
When TAMPxTRG = 1: if the TAMPERx alternate function is already low before tamper
detection is enabled, a tamper event is detected as soon as TAMPERx is enabled
(even if there was no falling edge on TAMPERx after TAMPxE was set.
After a tamper event has been detected and cleared, the TAMPERx alternate function
should be disabled and then re-enabled (TAMPxE set to 1) before re-programming the
backup registers (RTC_BKPxR). This prevents the application from writing to the backup
registers while the TAMPERx value still indicates a tamper detection. This is equivalent to a
level detection on the TAMPERx alternate function.
Note: Tamper detection is still active when V
of the backup registers, the pin to which the TAMPER alternate function is mapped should
be externally tied to the correct level.
TAMPER alternate function detection
The TAMPER1 alternate function 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 22.6.13: RTC tamper and alternate function configuration register
TAMPE bit must be cleared when TAMP1INSEL is modified to avoid unwanted setting of
TAMPF.
22.3.12

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 PREDIV_A = 0x7F, the RTC_CALIB frequency is f
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.
Calibration alternate function output
When the COE bit in the RTC_CR register is set to 1, the calibration alternate function
(AFO_CALIB) is enabled on RTC_AF1.
Note: When RTC_CALIB or RTC_ALARM is selected, RTC_AF1 is automatically configured in
output alternate function.
580/1378
power is switched off. To avoid unwanted resetting
DD
RM0033 Rev 8
RM0033
(RTC_TAFCR)).
.
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RTCCLK