PCF8564A datasheet(12/44 Pages) NXP

12 / 44 page

PCF8564A_1

Product data sheet

Rev. 1 — 8 October 2009

12 of 44

NXP Semiconductors

PCF8564A

Real time clock and calendar

8.4.7 Register Years

[1]

When the register Years overﬂows from 99 to 00, the century bit C in the register Months is toggled.

The PCF8564A compensates for leap years by adding a 29th day to February if the year

counter contains a value which is divisible by 4, including the year 00.

8.5 Setting and reading the time

Figure 6 shows the data ﬂow and data dependencies starting from the 1 Hz clock tick.

During read/write operations, the time counting circuits (memory locations 02h through

08h) are blocked.

This prevents

• Faulty reading of the clock and calendar during a carry condition

• Incrementing the time registers, during the read cycle

After this read/write access is completed, the time circuit is released again and any

pending request to increment the time counters, that occurred during the read access, is

serviced. A maximum of 1 request can be stored; therefore, all accesses must be

completed within 1 second (see Figure 7).

Table 17.

Years - years register (08h) bit description

Bit

Symbol

Value

Place value Description

7 to 4 YEARS

0 to 9

ten’s place

actual year coded in BCD format[1]

3 to 0

0 to 9

unit place

Fig 6.

Data ﬂow for the time function

013aaa092

1 Hz tick

WEEKDAY

SECONDS

MINUTES

HOURS

DAYS

LEAP YEAR

CALCULATION

MONTHS

YEARS

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