PCF2123 datasheet(17/54 Pages) NXP

17 / 54 page

PCF2123_1

Product data sheet

Rev. 01 — 19 November 2008

17 of 54

NXP Semiconductors

PCF2123

SPI Real time clock/calendar

9.6.1 Data ﬂow

Figure 11 shows the data ﬂow and data dependencies starting from the 1 Hz clock tick.

In order to read the correct time it is important to read all time registers in one access i.e.

seconds up to years. If the time registers are read by making individual access to the chip,

then there is the risk that the time will increment between accesses.

9.7 Alarm function

When one or more of these registers are loaded with a valid minute, hour, day or weekday

and its corresponding alarm enable not bit (AEN_x) is logic 0, then that information will be

compared with the current minute, hour, day and weekday.

[1]

Values shown in decimal.

Fig 11. Data ﬂow for the time function

001aaf901

1 Hz tick

12_24 hour mode

WEEKDAY

SECONDS

MINUTES

HOURS

DAYS

LEAP YEAR

CALCULATION

MONTHS

YEARS

Table 18.

Bit

Symbol

Value

Description

AEN_M

minute alarm is enabled

minute alarm is disabled

6 to 0

MINUTE_ALARM 00 to 59[1]

this register holds the minute alarm information coded in

BCD format

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