PCF8593 datasheet(23/28 Pages) PHILIPS

23 / 28 page

1997 Mar 25

Philips Semiconductors

Product speciﬁcation

Low power clock/calendar

PCF8593

14 APPLICATION INFORMATION

14.1

Quartz frequency adjustment

14.1.1

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 1 Hz signal which can

be programmed to occur at the interrupt output (pin 7). The

frequency tolerance depends on the quartz crystal

tolerance, the capacitor tolerance and the

device-to-device tolerance (on average

±5 × 10−6).

Average deviations of

±5 minutes per year can be

achieved.

14.1.2

METHOD 2: OSCI TRIMMER

Using the alarm function (via the I2C-bus) a signal faster

than 1 Hz can be generated at the interrupt output for fast

setting of a trimmer.

Procedure:

• Power-on

• Apply RESET

• Initialization (alarm functions).

Routine:

• Set clock to time T and set alarm to time T + ∆T

• At time T + ∆T (interrupt) repeat routine.

14.1.3

METHOD 3: DIRECT OUTPUT

Direct measurement of oscillator output (accounting for

test probe capacitance).

Fig.23 Application diagram.

(1) Example Philips DLC 196 Double-Layer Capacitor family.

handbook, full pagewidth

MBD825

RESET

SCL

SDA

V SS

OSCI

OSCO

CLOCK CALENDAR

PCF8593

SDA

SCL

MASTER

TRANSMITTER/

RECEIVER

RESET

V DD

SDA

SCL

V DD

(I C-bus)

R: pull-up resistor

R =

(1)

1 F

C BUS

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