PCF8563_6

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 06 — 21 February 2008

5 of 32

NXP Semiconductors

PCF8563

Real-time clock/calendar

7.2 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 frequencies for

⁄

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 (on pin INT). The interrupt may be

generated as a pulsed signal every countdown period or as a permanently active signal

which follows the state of TF. Bit TI_TP is used to control this mode selection. When

reading the timer, the current countdown value is returned.

7.3 Clock 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.

7.4 Reset

The PCF8563 includes an internal reset circuit which is active whenever the oscillator is

according to Table 25.

7.5 Voltage-low detector

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

This will indicate that the time may be corrupted.

Fig 7.

Voltage-low detection

VL set

normal power

operation

period of battery

operation

t

mgr887