Philips Semiconductors

PCF8563

Real-time clock/calendar

Product specification

16 April 1999

11 of 30

9397 750 04855

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

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

timer clock.

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

Bit

Symbol

Description

7

FE

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

1

FD1

pin; see Table 24.

0

FD0

Table 24: CLKOUT frequency selection

FD1

FD0

0

0

32.768 kHz

0

1

1 024 Hz

1

0

32 Hz

11

1 Hz

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

Bit

Symbol

Description

7

TE

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

6to2

−

not implemented

1

TD1

Timer source clock frequency selection bits. These bits determine

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

saving.

0

TD0

Table 26: Timer source clock frequency selection

TD1

TD0

Timer source clock frequency (Hz)

0

0

4096

01

64

10

1

11

1

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

Bit

Symbol

Description

7 to 0

<timer countdown value>

This register holds the loaded countdown value ‘n’.

Countdown period

n

Source clock frequency

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