PCF8523 datasheet(19/66 Pages) NXP

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PCF8523

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Product data sheet

Rev. 3 — 30 March 2011

19 of 66

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

8.6 Time and date registers

Most of these registers are coded in the Binary Coded Decimal (BCD) format. BCD is

used to simplify application use. An example is shown for the array SECONDS in

Table 11.

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 will remain

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 10.

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 11.

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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