AN3133 datasheet(8/43 Pages) STMICROELECTRONICS

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Real-time clock overview

AN3133

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Doc ID 16956 Rev 5

Example 1: If the user performs a negative shift in time of 100ms (to reach 03h25’32’’400),

he must subtract “102” subseconds (102 = 100 ms * 32768 / 32). This means that the sub-

second[15:0] field will be equal to 613 (511–(–102)).

This operation is performed by configuring:

–

RTC_SHIFTRH_ADD1S = 0 and

–

RTC_SHIFTRx_SUBFS[14:0] = 102

Example 2: If the user performs a positive shift in time of 100 ms (to reach the equivalent

03'25''32°600), he must add 1s–(1023-102 +1) sub-seconds, which means that the sub-

second[15:0] field will be equal to 1433 (511–(–(1023–102+1))) and the seconds field will be

equal to 33 (32+1). In this case, the user must take care about the fact that he will not read

3h25’32 in the time register right after the shift operation. He will read 3h25’33, with a sub-

second value = 1433

This operation is performed by configuring:

–

RTC_SHIFTRH_ADD1S = 1 and

–

RTC_SHIFTRx_SUBFS[14:0] = 1023 – 102 + 1 = 922

1.2

RTC alarm

An alarm can be generated at a given time or/and date programmed by the user.

The STM8L/STM8AL RTC provides a rich combination of alarms, and offers many features

to easily configure, and display these alarms:

●

Full programmable alarm: sub-seconds, seconds, minutes, hours and date fields can

be independently selected or masked to provide the user a rich combination of alarms.

●

Ability to exit the device from Active-halt mode when the alarm occurs.

●

The alarm event can be routed to a specific output pad with configurable polarity.

●

Dedicated alarm flag and interrupt.

Figure 3.

RTC alarm fields

RTC_ALRMARx and RTC_ALRMASSRx are RTC registers.

MSKx and MASKSS[3:0] are bits in the RTC_ALARMx and RTC_ALRMASSMSKR registers which

enable/disable the RTC_ALARMx fields used for alarm and calendar comparison. For more details refer to

Table 8.

ALARM

Alarm date

12h or 24h

format

ai17263

- Day of week

- Date

- AM

- PM

Day of week

/Date

Alarm time

RTC_ALRMAR4

RTC_ALRMAR3 RTC_ALRMAR2

RTC_ALRMASSRx

MSK4

MSK3

MSK2

RTC_ALRMAR1

MSK1

MASKSS[3:0]

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