Philips Semiconductors

PCF8563

Real-time clock/calendar

Product specification

16 April 1999

21 of 30

9397 750 04855

© Philips Electronics N.V. 1999. All rights reserved.

12. Application information

12.1 Quartz crystal frequency adjustment

Method 1: Fixed OSCI capacitor — By evaluating the average capacitance

necessary for the application layout a fixed capacitor can be used. The frequency is

best measured via the 32.768 kHz signal available after power-on at the CLKOUT

pin. The frequency tolerance depends on the quartz crystal tolerance, the capacitor

tolerance and the device-to-device tolerance (on average

Average deviations of

±5 minutes per year can be easily achieved.

Method 2: OSCI trimmer — The oscillator is tuned to the required accuracy by

adjusting a trimmer capacitor on pin OSCI and measuring the 32.768 kHz signal

available after power-on at the CLKOUT pin.

Method 3: OSCO output — Direct output measurement on pin OSCO (accounting

for test probe capacitance).

Fig 19. Application diagram.

handbook, full pagewidth

MGM665

SCL

SDA

VSS

OSCI

OSCO

CLOCK CALENDAR

PCF8563

SDA

SCL

MASTER

TRANSMITTER/

RECEIVER

VDD

VDD

SDA

SCL

RR

VDD

R: pull-up resistor

R =

1 F

tr

Cb