PCF8563 datasheet(11/30 Pages) PHILIPS

11 / 30 page

Philips Semiconductors

PCF8563

Real-time clock/calendar

Product speciﬁcation

16 April 1999

11 of 30

9397 750 04855

8.6.6

CLKOUT frequency register

8.6.7

Countdown timer registers

The Timer register is an 8-bit binary countdown timer. It is enabled and disabled via

the Timer control register bit TE. The source clock for the timer is also selected by the

Timer control register. Other timer properties, e.g. interrupt generation, are controlled

via the Control/status 2 register. For accurate read back of the countdown value, the

I2C-bus clock SCL must be operating at a frequency of at least twice the selected

timer clock.

Table 23: CLKOUT frequency register bits description (address 0DH)

Bit

Symbol

Description

FE = 0; the CLKOUT output is inhibited and the CLKOUT output is

set to high-impedance. FE = 1; the CLKOUT output is activated.

6to2

−

not implemented

FD1

These bits control the frequency output (fCLKOUT) on the CLKOUT

pin; see Table 24.

FD0

Table 24: CLKOUT frequency selection

FD1

FD0

fCLKOUT

32.768 kHz

1 024 Hz

32 Hz

1 Hz

Table 25: Timer control register bits description (address 0EH)

Bit

Symbol

Description

TE = 0; timer is disabled. TE = 1; timer is enabled.

6to2

−

not implemented

TD1

Timer source clock frequency selection bits. These bits determine

the source clock for the countdown timer, see Table 26. When not

in use, TD1 and TD0 should be set to ‘11’ (1

⁄60 Hz) for power

saving.

TD0

Table 26: Timer source clock frequency selection

TD1

TD0

Timer source clock frequency (Hz)

4096

⁄60

Table 27: Timer countdown value register bits description (address 0FH)

Bit

Symbol

Description

7 to 0

This register holds the loaded countdown value ‘n’.

Countdown period

Source clock frequency

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