PCF8523 NXP [NXP Semiconductors], PCF8523 Datasheet - Page 6

• Manufacturer Part Number: PCF8523
• Description: Real-Time Clock (RTC) and calendar
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
8. Functional description
PCF8523
Product data sheet
The PCF8523 contains
All 20 registers are designed as addressable 8-bit registers although not all bits are
implemented.
The registers Seconds, Minutes, Hours, Days, Weekdays, Months, and Years are all
coded in Binary Coded Decimal (BCD) format. Other registers are either bit-wise or
standard binary. When one of the RTC registers is read, the contents of all counters are
frozen. Therefore, faulty reading of the clock and calendar during a carry condition is
prevented.
The PCF8523 has a battery backup input pin and battery switch-over circuit, which
monitors the main power supply and automatically switches to the backup battery when a
power failure condition is detected. Accurate timekeeping is maintained even when the
main power supply is interrupted.
A battery low detection circuit monitors the status of the battery. When the battery voltage
goes below a certain threshold value, a flag is set to indicate that the battery must be
replaced soon. This ensures the integrity of the data during periods of battery backup.
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20 8-bit registers with an auto-incrementing address register,
An on-chip 32.768 kHz oscillator with two integrated load capacitors,
A frequency divider, which provides the source clock for the Real-Time Clock (RTC),
A programmable clock output,
A 1 Mbit/s I
And an offset register, which allows fine-tuning of the clock.
The first three registers (memory address 00h, 01h, and 02h) are used as control and
status registers.
The addresses 03h through 09h are used as counters for the clock function (seconds
up to years).
Addresses 0Ah through 0Dh define the alarm condition.
Address 0Eh defines the offset calibration.
Address 0Fh defines the clock-out mode and the addresses 10h and 12h the timer
mode.
Addresses 11h and 13h are used for the timers.
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All information provided in this document is subject to legal disclaimers.
C-bus interface,
Rev. 3 — 30 March 2011
Real-Time Clock (RTC) and calendar
PCF8523
© NXP B.V. 2011. All rights reserved.
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