PCF8564A datasheet(16/44 Pages) NXP

16 / 44 page

PCF8564A_1

Product data sheet

Rev. 1 — 8 October 2009

16 of 44

NXP Semiconductors

PCF8564A

Real time clock and calendar

[1]

Default value.

8.8 Timer function

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

the timer (4.096 kHz, 64 Hz, 1 Hz, or 1

⁄

60 Hz) and enables or disables the timer. The timer

counts down from a software-loaded 8-bit binary value. At the end of every countdown,

the timer sets the TF (Timer Flag) to logic 1. The TF may only be cleared using the

interface.

The generation of interrupts from the timer function is controlled via bit TIE. If bit TIE is

enabled the INT pin follows the condition of bit TF. The interrupt may be generated as a

pulsed signal every countdown period or as a permanently active signal which follows the

condition of the timer ﬂag TF. TI_TP is used for this mode control. When reading the timer,

the current countdown value is returned.

8.8.1 Register Timer_ctrl

[1]

Default value.

[2]

These bits determine the source clock for the countdown timer; when not in use, TD[1:0] should be set to

⁄60 Hz for power saving.

Table 22.

CLKOUT_ctrl - CLKOUT control register (address 0Dh) bit description

Bit

Symbol

Value

Description

the CLKOUT output is inhibited and CLKOUT output is

set to logic 0

1[1]

the CLKOUT output is activated

6 to 2 -

unused

1 to 0 FD[1:0]

frequency output at pin CLKOUT

00[1]

32.768 kHz

1.024 kHz

32 Hz

1 Hz

Table 23.

Timer_ctrl - timer control register (address 0Eh) bit description

Bit

Symbol

Value

Description

7TE

0[1]

timer is disabled

timer is enabled

6 to 2 -

unused

1 to 0 TD[1:0]

timer source clock frequency select[2]

4.096 kHz

64 Hz

1 Hz

11[2]

⁄60 Hz

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