PCF8564AUSLASH5BDSLASH1 datasheet(13/44 Pages) NXP

13 / 44 page

PCF8564A_1

Product data sheet

Rev. 1 — 8 October 2009

13 of 44

NXP Semiconductors

PCF8564A

Real time clock and calendar

As a consequence 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 may 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.

Recommended method for reading the time:

1. Send a START condition and the slave address for write (A2h).

2. Set the address pointer to 2 (seconds) by sending 02h.

3. Send a RE-START condition or STOP followed by START.

4. Send the slave address for read (A3h).

5. Read the seconds.

6. Read the minutes.

7. Read the hours.

8. Read the days.

9. Read the weekdays.

10. Read the century and month.

11. Read the years.

12. Send a STOP condition.

8.6 Alarm registers

8.6.1 Register Minute_alarm

[1]

Default value.

Fig 7.

Access time for read/write operations

START

slave address

data

STOP

t < 1 s

013aaa215

Table 18.

Minute_alarm - minute alarm register (address 09h) 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

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