PCF2123 datasheet(20/63 Pages) NXP

20 / 63 page

PCF2123

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Product data sheet

Rev. 5 — 27 April 2011

20 of 63

NXP Semiconductors

PCF2123

SPI Real time clock/calendar

8.6 Timer functions

The countdown timer has four selectable source clocks allowing for countdown periods in

the range from 244

μs to 4 h 15 min. There are also two pre-defined timers which can be

used to generate an interrupt once per second or once per minute. For periods greater

than 4 hours, the alarm function can be used. Registers 01h, 0Eh and 0Fh are used to

control the timer function and output.

8.6.1 Register Timer_clkout

[1]

Values of COF[2:0] see Table 35.

[2]

Default value.

8.6.2 Register Countdown_timer

8.6.3 Minute and second interrupt

The minute and second interrupts (bits MI and SI) are pre-defined timers for generating

periodic interrupts. The timers can be enabled independently from one another. However,

a minute interrupt enabled on top of a second interrupt will not be distinguishable since it

will occur at the same time; see Figure 14.

Table 24.

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

Bit

Symbol

Value

Description

Reference

unused

6 to 4 COF[2:0]

[1]

CLKOUT control

Section 8.8

countdown timer is disabled

Section 8.6.4

countdown timer is enabled

unused

1 to 0 CTD[1:0]

4.096 kHz countdown timer source clock

64 Hz countdown timer source clock

1 Hz countdown timer source clock

11[2]

⁄

60 Hz countdown timer source clock

Table 25.

Countdown_timer - countdown timer register (address 0Ah) bit description

Bit

Symbol

Value

Description

Reference

7 to 0

COUNTDOWN_TIMER[7:0]

0h to FFh

countdown period in seconds:

where n is the countdown value

Section 8.6.4

CountdownPeriod

SourceClockFrequency

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