PCF2127ATSLASH1 datasheet(6/80 Pages) NXP

6 / 80 page

PCF2127A_2

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Product data sheet

Rev. 02 — 7 May 2010

6 of 80

NXP Semiconductors

PCF2127A

Integrated RTC, TCXO and quartz crystal

8.1 Register overview

The PCF2127A contains 30 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. The registers 1Ch and 1Dh must be addressed directly (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 8.9).

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

interrupt is generated when an alarm event occurs (see Section 8.10).

• 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 and countdown timer

functions. The timer has four selectable source clocks allowing for timer periods from

less than 1 ms to greater than 4 hours (see Table 36). Either the watchdog timer or

the countdown timer can be enabled (see Section 8.11). For the watchdog timer it is

possible to select whether an interrupt or a pulse on the reset pin will be generated

when the watchdog times out. For the countdown timer it is only possible that an

interrupt will be generated at the end of the countdown.

• 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 8.12).

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

Section 8.4.1).

Fig 3.

Handling address registers

001aaj307

address register

00h

auto-increment

wrap around

01h

02h

03h

...

19h

1Ah

1Bh

1Ch

1Dh

not reachable by auto-inc. - needs to be addressed directly

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