PCF2129A_10 datasheet(6/69 Pages) NXP

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PCF2129A_2

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Product data sheet

Rev. 02 — 7 May 2010

6 of 69

NXP Semiconductors

PCF2129A

Integrated RTC, TCXO and quartz crystal

8.1 Register overview

The PCF2129A contains 28 8-bit registers (see Table 4) with an auto-incrementing

address register: the built-in address register will increment automatically after each read

or write of a data byte up to the register 1Bh. After register 1Bh the auto-incrementing will

wrap around to address 00h (see Figure 3).

• The first three registers (memory address 00h, 01h, and 02h) are used as control

registers (see Section 8.2).

• The memory addresses 03h through to 09h are used as counters for the clock

function (seconds up to years). The date is automatically adjusted for months with

fewer than 31 days, including corrections for leap years. The clock can operate in

12-hour mode with an AM/PM indication or in 24-hour mode (see Section 8.8).

• Addresses 0Ah through 0Eh define the alarm function. It can be selected that an

interrupt is generated when an alarm event occurs (see Section 8.9).

• The register 0Fh defines the temperature measurement period and the clock out

mode. The temperature measurement can be selected from every 4 minutes (default)

down to every 30 seconds (see Table 9). CLKOUT frequencies of 32.768 kHz

(default) down to 1 Hz for use as a system clock, a microcontroller clock etc. can be

chosen (see Table 10).

• Address registers 10h and 11h are used for the watchdog timer functions. The

watchdog timer has four selectable source clocks allowing for timer periods from less

than 1 ms to greater than 4 hours (see Table 32). An interrupt will be generated when

the watchdog times out.

• Address registers 12h to 18h are used for the timestamp function. When the trigger

event happens, the actual time is saved in the timestamp registers (see Section 8.11).

• Address register 19h is used for the correction of the crystal aging effect (see

Section 8.4.1).

• Address registers 1Ah and 1Bh are for internal use only.

• The registers Seconds, Minutes, Hours, Days, Months, and Years are all coded in

Binary Coded Decimal (BCD) format to simplify application use. Other registers are

either bit-wise or standard binary.

When one of the RTC registers is written or read, the content of all counters is temporarily

frozen. This prevents a faulty writing or reading of the clock and calendar during a carry

condition (see Section 8.8.8).

Fig 3.

Handling address registers

001aaj398

address register

00h

auto-increment

wrap around

01h

02h

03h

...

19h

1Ah

1Bh

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