AS3543 datasheet(49/92 Pages) AMSCO

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AS3543 3v2

Data Sheet - D e t a i l e d D e s c r i p t i o n - S Y S T E M F u n c t i o n s

10.5

Real Time Clock

10.5.1 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. 650nA. (Q32K clock buffer not operating)

An internal supply switch will supply the RTC as long as possible form the Li-Ion battery and only switch to BVDDR if

the main battery is empty or has been removed.

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

second or minute 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.

The Q32K output can be configured to operate in push/pull (3 different driver strengths) or to be trie-state. For a more

detailed description of the GPIO functionality of this pin please refer to chapter GPIO Pins on page 50.

10.5.2 Clock Adjustment

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

quency 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]

10.5.3 Register Description

Table 36. RTC Related Register

Name

Base

Offset

Description

RAM & WakeUp

2-wire serial

19h

RTC wake-up settings and SDRAM access

Out_Cntr2

2-wire serial

1A-2h

Control of Q32K signal and drive

PMU_Enable

2-wire serial

1Ch

Enables writings to extended register 1Ah-2

IRQENRD_2

2-wire serial

25h

Interrupt settings for RVDD under-voltage detection

IRQENRD_4

2-wire serial

27h

Interrupt settings for getting a second or minute interrupt

RTC_Cntr

2-wire serial

28h

RTC oscillator and counter enable, free usable bits

RTC_Time

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

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