PCF8523TSLASH1 datasheet(32/75 Pages) NXP

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PCF8523

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Product data sheet

Rev. 4 — 5 July 2012

32 of 74

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

8.9 Timer function

The PCF8523 has three timers:

• Timer A can be used as a watchdog timer or a countdown timer (see Section 8.9.2). It

can be configured by using TAC[1:0] in the Tmr_CLKOUT_ctrl register (0Fh)

• Timer B can be used as a countdown timer (see Section 8.9.3). It can be configured

by using TBC in the Tmr_CLKOUT_ctrl register (0Fh)

• Second interrupt timer is used to generate an interrupt once per second (see

Section 8.9.4)

Timer A and timer B both have five selectable source clocks allowing for countdown

periods from less than 1 ms to 255 h. To control the timer functions and timer output, the

registers 01h, 0Fh, 10h, 11h, 12h, and 13h are used.

8.9.1 Timer registers

8.9.1.1

[1]

Default value.

8.9.1.2

CLKOUT frequency selection

Clock output operation is controlled by the COF[2:0] in the Tmr_CLKOUT_ctrl register.

Frequencies of 32.768 kHz (default) down to 1 Hz can be generated (see Table 35) for

use as a system clock, microcontroller clock, input to a charge pump, or for calibration of

the oscillator.

Table 34.

Tmr_CLKOUT_ctrl - timer and CLKOUT control register (address 0Fh) bit

description

Bit

Symbol

Value

Description

7TAM

0[1]

permanent active interrupt for timer A and for

the second interrupt timer

pulsed interrupt for timer A and the second

interrupt timer

6TBM

0[1]

permanent active interrupt for timer B

pulsed interrupt for timer B

5 to 3

COF[2:0]

see Table 35

CLKOUT frequency selection

2 to 1

TAC[1:0]

00[1] to 11

timer A is disabled

timer A is configured as countdown timer

if CTAIE (register Control_2) is set logic 1, the

interrupt is activated when the countdown

timed out

timer A is configured as watchdog timer

if WTAIE (register Control_2) is set logic 1,

the interrupt is activated when timed out

0TBC

0[1]

timer B is disabled

timer B is enabled

if CTBIE (register Control_2) is set logic 1, the

interrupt is activated when the countdown

timed out

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