Datasheet

Product data sheet Rev. 6 — 17 September 2013 24 of 78

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 rollover may occur between reads

thus giving the minutes from one moment and the hours from the next.

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 7

Table 22. Minute_alarm - minute alarm register (address 0Ah) bit description

Bit Symbol Value Place value Description

7 AEN_M 0 - minute alarm is enabled

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

Bit Symbol Value Place value Description

7 AEN_H 0 - hour alarm is enabled

[1]

- hour alarm is disabled

6 - - - unused

12 hour mode

[2]

5 AMPM 0 - indicates AM

1 - indicates PM

4 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 0to9 unit place