PCF8563TSLASHF4 datasheet(16/45 Pages) NXP

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PCF8563

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Product data sheet

Rev. 11 — 26 October 2015

16 of 45

NXP Semiconductors

PCF8563

Real-time clock/calendar

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 (4096 Hz, 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 timer flag TF. The TF may only be cleared by using the interface. The

asserted TF can be used to generate an interrupt on pin INT. The interrupt may be

generated as a pulsed signal every countdown period or as a permanently active signal

which follows the state of TF. Bit TI_TP is used to control this mode selection. When

reading the timer, the current countdown value is returned.

8.8.1 Register Timer_control

[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

1⁄60 Hz for power saving.

8.8.2 Register Timer

The register Timer 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 such as interrupt generation are controlled

via the register Control_status_2.

For accurate read back of the count down value, it is recommended to read the register

twice and check for consistent results, since it is not possible to freeze the countdown

timer counter during read back.

Table 23.

Timer_control - 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]

1⁄60 Hz

Table 24.

Timer - timer value register (address 0Fh) bit description

Bit

Symbol

Value

Description

7 to 0

TIMER[7:0]

00h to FFh

countdown period in seconds:

where n is the countdown value

Table 25.

Timer register bits value range

Bit

128

8421

CountdownPeriod

SourceClockFrequency

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