AS3517H-ECTP datasheet(53/94 Pages) AMSCO

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AS3517 V17

Data Sheet, Confidential

www.austriamicrosystems.com

9.3.5

Real Time Clock

General

The real time clock block is an independent block, which is still working even when the chip is shut down. The only condition for this

operation is that BVDDR has a voltage of above 1.0V. The block uses a standard 32kHz crystal that is connected to a low power

oscillator. The total power consumption is typ. 12µA. (Q32k clock buffer not operating)

The RTC seconds counter is 32bit wide and can be programmed via the 2-wire serial interface. The RTC can deliver a seconds or minutes

interrupt.

Another 23bit wide counter allows auto wake-up (max. after 96 days). This counter is internally connected to the power-up and hibernation

control block.

The RTC voltage regulator (RVDD) further supplies a 128bit SRAM. It can be used to store settings or data before shutdown.

Clock adjustment

The RTC clock is adjustable in steps of 7.6ppm which allows the use of inexpensive 32kHz crystals. The nominal frequency shall be

32.768Hz. This frequency is divided down to 0.25Hz:

f = 32.768 / (4*32*1024)

At the input of this divider one can add corrective counts, which allow to correct an inaccurate crystal in a range from –64 counts (=-

488ppm) to +63 counts (=+480ppm):

fcorrected = fcrystal / [(4*32*1024)-64+RTC_TBC]

Table 41 RTC Related Register

Name

Base

Offset

Description

RTCV

2-wire serial

28h

RTC oscillator and counter enable

RTCT

2-wire serial

29h

RTC interrupt and time correction settings

RTC_0 to RTC_3

2-wire serial

2Ah to 2Dh

RTC time-base seconds registers

RTC_WakeUp

2-wire serial

19h

RTC wake-up settings and SDRAM access

IRQ_ENRD_2

2-wire serial

25h

Interrupt settings for RVDD under-voltage detection

IRQ_ENRD_4

2-wire serial

27h

Interrupt settings for getting a second or minute interrupt

Revision 1v3

- 93

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