PCF8523TSSLASH1 datasheet(20/75 Pages) NXP

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PCF8523

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Product data sheet

Rev. 4 — 5 July 2012

20 of 74

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

8.6.1 Register Seconds

[1]

Start-up value.

8.6.1.1

Oscillator STOP flag

The OS flag is set whenever the oscillator is stopped (see Figure 12). The flag remains

set until cleared by using the interface. When the oscillator is not running, then the OS flag

cannot be cleared. This method can be used to monitor the oscillator.

The oscillator may be stopped, for example, by grounding one of the oscillator pins, OSCI

or OSCO. The oscillator is also considered to be stopped during the time between

power-on and stable crystal resonance. This time may be in a range of 200 ms to 2 s,

depending on crystal type, temperature, and supply voltage. At power-on, the OS flag is

always set.

Table 12.

Seconds - seconds and clock integrity status register (address 03h) bit

description

Bit

Symbol

Value

Place value Description

clock integrity is guaranteed

1[1]

clock integrity is not guaranteed;

oscillator has stopped or been

interrupted

6 to 4

SECONDS

0 to 5

ten’s place

actual seconds coded in BCD

format

3 to 0

0 to 9

unit place

Table 13.

SECONDS coded in BCD format

Seconds value in

decimal

Upper-digit (ten’s place)

Digit (unit place)

Bit

000

0000

000

0001

000

0010

:::

::::

000

1001

001

0000

:::

::::

101

1000

101

1001

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