AN3133 datasheet(12/43 Pages) STMICROELECTRONICS

12 / 43 page

Real-time clock overview

AN3133

12/43

Doc ID 16956 Rev 5

Digital filtering is performed by configuring the number of identical and consecutive active

levels which must be detected in order to generate a tamper event, and an interrupt which

will wake up the device from Active-halt mode. The number of consecutive active levels

before issuing an event can be 1, 2, 4 or 8.

Figure 7.

Example of tamper filtering

Tamper is set after 2 consecutive samples at the active level.

Figure 7 shows a tamper detection with the following configuration:

●

TAMPxLEVEL = 0x1: High level

●

TAMPFREQ = 0x0: Tamper sampling frequency = 1 Hz

●

TAMPPRCH = 0x1: Tamper precharge duration = 2 cycles

●

TAMPFLT = 0x1: Tamper filter count = 2 consecutive samples

1.6

RTC and low-power consumption

The STM8L/STM8AL RTC is designed to minimize the power consumption. The prescalers

used for the calendar are divided in 2: synchronous and asynchronous.

Increasing the value of the asynchronous prescaler reduces the power consumption.

The RTC continues working in reset mode and its registers are not reset except by a Power-

on reset. RTC registers values are not lost after a reset and the calendar keeps the correct

time and date.

After a system reset or a power-on reset, the device operates in Run mode. In addition, the

device supports five low power modes to achieve the best compromise between low power

consumption, short startup time and available wakeup sources.

The RTC peripheral can be active in the following low power modes:

●

Wait

●

Low Power Run

●

Low Power Wait

●

Active-halt

The RTC cannot wake up the device from Low Power Run and Low Power Wait mode since

there is no associated event.

RTCCLK

TamperDet_03

RTC_TAMPx

Switch Closed

Switch Open

TAMPPRCH = 0x1 (2 cycles)

Sampled level: 0

Sampled level: 1

TAMPFREQ = 0x0 (1 s)

TAMPxF interrupt

TAMPFLT = 0x1

(1)

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