PCF8523 datasheet(12/66 Pages) NXP

12 / 66 page

PCF8523

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Product data sheet

Rev. 3 — 30 March 2011

12 of 66

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.

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