WM8352 datasheet(190/336 Pages) WOLFSON

190 / 336 page

WM8352

Production Data

PD, February 2011, Rev 4.4

190

The current time can be read from the registers defined above. As the content of the time registers

changes every second, a single register read, executed at an arbitrary time, does not guarantee an

accurate time reading. Two possible methods are recommended for reliable reading of the time

registers:



Read after interrupt: the RTC_SEC interrupt (see Section 22.5) indicates that the seconds

counter has just been incremented, and that the RTC registers will not change again within

the next 999ms. A register read executed immediately after an RTC_SEC interrupt can

therefore be taken as an accurate time reading.



Two consecutive reads: if two consecutive reads within a short time (less than 1s apart)

return the same result, this can be taken as an accurate reading. If the two results differ,

the procedure should be repeated.

22.2.3

SETTING THE TIME

When writing to the RTC time registers, the seconds counter should first be stopped in order to

prevent glitches. The following procedure should be used:



Set the RTC_SET bit to stop seconds counter



Read the RTC_STS bit. Repeat this step until RTC_STS=1



Set new time in Registers R16 to R19



Clear the RTC_SET bit to re-enable seconds counter.

The RTC_SET and RTC_STS bits are defined in Table 132.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R23 (17h)

RTC Time

control

RTC_SET

Stops RTC seconds counter (instruction only)

0 = normal operation

1 = stop counter

RTC_STS

Status of RTC seconds counter

0 = normal operation

1 = counter stopped

Table 132 Setting the RTC Time

22.2.4

RTC ALARM REGISTERS

An RTC Alarm can be set by writing to the control fields in registers R20 to R22, which are in a

similar format to the RTC Time registers.

Setting any of these fields to “All 1’s” results in that field being a “don’t care” field. For example,

setting the RTC_ALMDAY field to 0001 determines that the alarm is set for a Sunday, whilst setting

RTC_ALMDAY to 1111 results in the programmed alarm occurring on every day of the week.

When the RTC Alarm time/date fields match the RTC time, the alarm event is signalled by the

WM8352 raising the RTC_ALM_EINT interrupt. See Section 22.5 for further details.

WM8352 Datasheet(PDF) 190 Page - Wolfson Microelectronics plc

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