PCF8564A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 26 August 2013 5 of 48
NXP Semiconductors
PCF8564A
Real time clock and calendar
8. Functional description
The PCF8564A contains sixteen 8-bit registers with an auto-incrementing address
register, an on-chip 32.768 kHz oscillator with integrated capacitors, a frequency divider
which provides the source clock for the RTC, a programmable clock output, a timer, a
voltage low detector, and a 400 kHz I
2
C-bus interface.
All sixteen registers (see Table 5
) 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, months, years, as well as the minute alarm, hour
alarm, and day 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.
