PCF8523 datasheet(23/66 Pages) NXP

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PCF8523

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Product data sheet

Rev. 3 — 30 March 2011

23 of 66

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

Because of this method, it is very important to make a read or write access in one go, that

is, setting or reading seconds through to years should be made in one single access.

Failing to comply with this method could result in the time becoming corrupted.

As an example, if the time (seconds through to hours) is set in one access and then in a

second access the date is set, it is possible that the time will increment between the two

accesses. A similar problem exists when reading. A roll over may occur between reads

thus giving the minutes from one moment and the hours from the next. Therefore, it is

advised to read all time and date registers in one access.

8.7 Alarm registers

The registers at addresses 0Ah through 0Dh contain the alarm information.

8.7.1 Register Minute_alarm

[1]

Default value.

8.7.2 Register Hour_alarm

[1]

Default value.

[2]

Hour mode is set by bit 12_24 in register Control_1 (see Table 5).

Table 20.

Minute_alarm - minute alarm register (address 0Ah) bit description

Bit

Symbol

Value

Place value Description

AE_M

minute alarm is enabled

1[1]

minute alarm is disabled

6 to 4

MINUTE_ALARM

0 to 5

ten’s place

minute alarm information coded in

BCD format

3 to 0

0 to 9

unit place

Table 21.

Hour_alarm - hour alarm register (address 0Bh) bit description

Bit

Symbol

Value

Place value Description

AE_H

hour alarm is enabled

1[1]

hour alarm is disabled

unused

12 hour mode[2]

AMPM

indicates AM

indicates PM

HOUR_ALARM

0 to 1

ten’s place

hour alarm information in 12 hour

mode coded in BCD format

3 to 0

0 to 9

unit place

24 hour mode[2]

5 to 4

HOURS

0 to 2

ten’s place

hour alarm information in 24 hour

mode coded in BCD format

3to0

0to 9

unit place

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