PCF8564AU datasheet(12/48 Pages) NXP

12 / 48 page

PCF8564A

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Product data sheet

Rev. 3 — 26 August 2013

12 of 48

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 5 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 writing or 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 6).

Table 18.

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]

3to0

0to9

unit place

Fig 5.

Data flow for the time function

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