PCF8564A datasheet(5/45 Pages) NXP

5 / 45 page

PCF8564A

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Product data sheet

Rev. 02 — 30 September 2010

5 of 45

NXP Semiconductors

PCF8564A

Real time clock and calendar

Functional description

The PCF8564A contains sixteen 8-bit registers with an auto-incrementing address

which provides the source clock for the RTC, a programmable clock output, a timer, a

voltage low detector, and a 400 kHz I2C-bus interface.

All sixteen registers (see Table 4) are designed as addressable 8-bit parallel registers

although not all bits are implemented. The first two registers (memory address 00h and

01h) are used as control and/or status registers. The addresses 02h through 08h are used

as counters for the clock function (seconds up to years counters). Address locations 09h

through 0Ch contain alarm registers which define the conditions for an alarm. Address

0Dh controls the CLKOUT output frequency. 0Eh and 0Fh are the timer control and timer

registers, respectively.

The seconds, minutes, hours, days, weekdays, months, years, as well as the minute

alarm, hour alarm, day alarm, and weekday alarm registers are all coded in BCD format.

8.1 CLKOUT output

A programmable square wave is available at the CLKOUT pin. Frequencies of

32.768 kHz, 1.024 kHz, 32 Hz and 1 Hz can be generated for use as a system clock,

microcontroller clock, input to a charge pump, or for calibration of the oscillator. CLKOUT

is a CMOS push-pull output, and if disabled it becomes logic 0.

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