PCA8565 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 4 — 5 December 2014 5 of 48
NXP Semiconductors
PCA8565
Real time clock/calendar
8. Functional description
The PCA8565 contains sixteen 8-bit registers with an auto-incrementing address register,
an on-chip 32.768 kHz oscillator with one integrated capacitor, a frequency divider which
provides the source clock for the Real Time Clock (RTC), a programmable clock output, a
timer, an alarm, a voltage-low detector and a 400 kHz I
2
C-bus interface.
All 16 registers are designed as addressable 8-bit registers although not all bits are
implemented:
• The first two registers (memory address 00h and 01h) are used as control and status
registers
• The registers at memory 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
• The register at address 0Dh controls the CLKOUT output frequency
• At address 0Eh is the timer control register and address 0Fh contains the timer value
The arrays SECONDS, MINUTES, HOURS, DAYS, WEEKDAYS, MONTHS, YEARS as
well as the bit fields MINUTE_ALARM, HOUR_ALARM, DAY_ALARM and
WEEKDAY_ALARM are all coded in Binary Coded Decimal (BCD) format.
When one of the RTC registers is written or read the contents of all time counters are
frozen. This prevents faulty writing or reading of the clock or calendar during a carry
condition (see Section 9.5.3
).
