PCF2127TSLASH2Y datasheet(7/100 Pages) PHILIPS

7 / 100 page

PCF2127

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Product data sheet

Rev. 8 — 19 December 2014

7 of 100

NXP Semiconductors

PCF2127

Accurate RTC with integrated quartz crystal for industrial applications

• The register at address 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 14). CLKOUT frequencies of

32.768 kHz (default) down to 1 Hz for use as system clock, microcontroller clock, and

so on, can be chosen (see Table 15).

• The registers at addresses 10h and 11h are used for the watchdog and countdown

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 58). 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

is generated when the watchdog times out. For the countdown timer, it is only

possible that an interrupt is generated at the end of the countdown.

• The registers at addresses 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).

• The register at address 19h is used for the correction of the crystal aging effect (see

Section 8.4.1).

• The registers at addresses 1Ah and 1Bh define the RAM address. The register at

address 1Ch (RAM_wrt_cmd) is the RAM write command; register 1Dh

(RAM_rd_cmd) is the RAM read command. Data is transferred to or from the RAM by

the serial interface (see Section 8.5).

• 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 8.9.8).

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