Philips Semiconductors

PCA8565

Real time clock/calender

Product data

Rev. 01 — 31 March 2003

4 of 26

9397 750 10695

© Koninklijke Philips Electronics N.V. 2003. All rights reserved.

8.1 Alarm function modes

By clearing the MSB of one or more of the alarm registers (bit AE = alarm enable),

the corresponding alarm condition(s) will be active. In this way an alarm can be

generated from once per minute up to once per week. The alarm condition sets the

Alarm Flag (AF). The asserted AF can be used to generate an interrupt (INT).

The AF can only be cleared by software.

8.2 Timer

The 8-bit countdown timer at address 0FH is controlled by the timer control register at

address 0EH. The timer control register determines one of 4 source clock

⁄

the timer. The timer counts down from a software-loaded 8-bit binary value. At the

end of every countdown, the timer sets the Timer Flag (TF). The TF may only be

cleared by software. The asserted TF can be used to generate an Interrupt (INT). The

interrupt may be generated as a pulsed signal every countdown period or as a

permanently active signal which follows the condition of TF. Bit TI/TP is used to

control this mode selection. When reading the timer, the current countdown value is

returned.

8.3 CLKOUT output

A programmable square wave is available at pin CLKOUT. Operation is controlled by

the CLKOUT control register at address 0DH. Frequencies of 32.768 kHz (default),

1024 Hz, 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 an open-drain output and enabled at power-on. If disabled it becomes

high-impedance.

8.4 Reset

The PCA8565 includes an internal reset circuit which is active whenever the oscillator

the address pointer, are cleared with the exception of bits FE, VL, TD1, TD0, TESTC

and AE which are set to logic 1.

8.5 Voltage-low detector

bit VL in the seconds register is set to indicate that the integrity of the clock

information is no longer guaranteed. The VL flag can only be cleared by software.

bit VL will be set. This will indicate that the time may be corrupted.