PCF8523USLASH12AASLASH1 datasheet(23/75 Pages) NXP

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PCF8523

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Product data sheet

Rev. 4 — 5 July 2012

23 of 74

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

8.6.7 Register Years

8.6.8 Data flow of the time function

Figure 13 shows the data flow and data dependencies starting from the 1 Hz clock tick.

During read/write operations, the time counting circuits (memory locations 03h through

09h) are blocked.

The blocking prevents:

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

• Incrementing the time registers during the read cycle

After the 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/write access

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

completed within 1 second (see Figure 14).

Table 21.

Years - years register (09h) bit description

Bit

Symbol

Value

Place value Description

7 to 4

YEARS

0 to 9

ten’s place

actual year coded in BCD format

3to0

0to 9

unit place

Fig 13. Data flow diagram of the time function

Fig 14. Access time for read/write operations

013aaa324

1 Hz tick

12/24 hour mode

WEEKDAYS

SECONDS

MINUTES

HOURS

DAYS

LEAP YEAR

CALCULATION

MONTHS

YEARS

t < 1 s

013aaa215

SLAVE ADDRESS

DATA

STOP

DATA

START

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