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PCF8523TS Schematic ( PDF Datasheet ) - NXP Semiconductors

Teilenummer PCF8523TS
Beschreibung Real-Time Clock (RTC) and calendar
Hersteller NXP Semiconductors
Logo NXP Semiconductors Logo 




Gesamt 30 Seiten
PCF8523TS Datasheet, Funktion
PCF8523
Real-Time Clock (RTC) and calendar
Rev. 3 — 30 March 2011
Product data sheet
1. General description
The PCF8523 is a CMOS1 Real-Time Clock (RTC) and calendar optimized for low power
consumption. Data is transferred serially via an I2C-bus with a maximum data rate of
1000 kbit/s. Alarm and timer functions are available with the possibility to generate a
wake-up signal on an interrupt pin. An offset register allows fine-tuning of the clock. The
PCF8523 has a backup battery switch-over circuit, which detects power failures and
automatically switches to the battery supply when a power failure occurs.
2. Features and benefits
Provides year, month, day, weekday, hours, minutes, and seconds based on a
32.768 kHz quartz crystal
Resolution: seconds to years
Clock operating voltage: 1.0 V to 5.5 V
Low backup current: typical 150 nA at VDD = 3.0 V and Tamb = 25 C
2 line bidirectional 1 MHz Fast-mode Plus (Fm+) I2C interface
Battery backup input pin and switch-over circuit
Freely programmable timer and alarm with interrupt capability
Selectable integrated oscillator load capacitors for CL = 7 pF or CL = 12.5 pF
Internal Power-On Reset (POR)
Open-drain interrupt or clock output pins
Programmable offset register for frequency adjustment
3. Applications
Time keeping application
Battery powered devices
Metering
1. The definition of the abbreviations and acronyms used in this data sheet can be found in Section 19.






PCF8523TS Datasheet, Funktion
NXP Semiconductors
PCF8523
Real-Time Clock (RTC) and calendar
8. Functional description
The PCF8523 contains
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 I2C-bus interface,
And an offset register, which allows fine-tuning of the clock.
All 20 registers are designed as addressable 8-bit registers although not all bits are
implemented.
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.
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.
PCF8523
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 30 March 2011
© NXP B.V. 2011. All rights reserved.
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PCF8523TS pdf, datenblatt
NXP Semiconductors
PCF8523
Real-Time Clock (RTC) and calendar
After reset, the following mode is entered:
32.768 kHz CLKOUT active
24 hour mode is selected
Register Offset is set logic 0
No alarms set
Timers disabled
No interrupts enabled
Battery switch-over is disabled
Battery low detection is disabled
7 pF of internal oscillator capacitor selected
8.4 Interrupt function
Active low interrupt signals are available at pin INT1/CLKOUT and INT2. Pin
INT1/CLKOUT has both functions of INT1 and CLKOUT combined.
INT1 Interrupt output may be sourced from different places:
Second timer
Timer A
Timer B
Alarm
Battery Switch-over
Battery Low Detection
Clock offset correction pulse
INT2 interrupt output is sourced only from timer B:
The control bit TAM (register Tmr_CLKOUT_ctrl) is used to configure whether the
interrupts generated from the second interrupt timer and timer A are pulsed signals or a
permanently active signal. The control bit TBM (register Tmr_CLKOUT_ctrl) is used to
configure whether the interrupt generated from timer B is a pulsed signal or a permanently
active signal. All the other interrupt sources generate a permanently active interrupt
signal, which follows the status of the corresponding flags.
The flags SF, CTAF, CTBF, AF, and BSF can be cleared by using the interface.
WTAF is read only. A read of the register Control_2 (01h) will automatically reset
WTAF (WTAF = 0) and clear the interrupt.
The flag BLF is read only. It is cleared automatically from the battery low detection
circuit when the battery is replaced.
PCF8523
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 3 — 30 March 2011
© NXP B.V. 2011. All rights reserved.
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