PCF2129 datasheet(30/86 Pages) PHILIPS

30 / 86 page

PCF2129

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Product data sheet

Rev. 7 — 19 December 2014

30 of 86

NXP Semiconductors

PCF2129

Accurate RTC with integrated quartz crystal for industrial applications

8.8.7 Register Years

8.8.8 Setting and reading the time

Figure 15 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.

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. Any pending

request to increment the time counters that occurred during the read/write access is

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

completed within 1 second (see Figure 16).

Table 36.

Years - years register (address 09h) bit allocation

Bits labeled as X are undefined at power-on and unchanged by subsequent resets.

Bit

Symbol

YEARS (0 to 99)

Reset

value

XXX

Table 37.

Years - years register (address 09h) bit description

Bits labeled as X are undefined at power-on and unchanged by subsequent resets.

Bit

Symbol

Value

Place value Description

7 to 4

YEARS

0 to 9

ten’s place

actual year coded in BCD format

3to0

0 to9

unit place

Fig 15. Data flow of the time function

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