PCF8564A datasheet(9/44 Pages) NXP

9 / 44 page

PCF8564A_1

Product data sheet

Rev. 1 — 8 October 2009

9 of 44

NXP Semiconductors

PCF8564A

Real time clock and calendar

8.4 Time and date registers

The majority of the registers are coded in the BCD format to simplify application use.

8.4.1 Register Seconds

[1]

Start-up value.

8.4.1.1

Voltage low detector and clock monitor

The PCF8564A has an on-chip voltage low detector. When VDD drops below Vlow the VL

(Voltage Low) ﬂag is set to indicate that the integrity of the clock information is no longer

guaranteed. The VL ﬂag can only be cleared by using the interface.

Table 8.

Seconds - seconds and clock integrity status register (address 02h) bit

description

Bit

Symbol

Value

Place value Description

clock integrity is guaranteed

1[1]

integrity of the clock information is not guaranteed

6 to 4 SECONDS 0 to 5

ten’s place

actual seconds coded in BCD format, see Table 9

3 to 0

0 to 9

unit place

Table 9.

Seconds coded in BCD format

Seconds value in

decimal

Upper-digit (ten’s place)

Digit (unit place)

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

0000000

0000001

0000010

0001001

0010000

1011000

1011001

Fig 5.

Voltage low detection

VL set

normal power

operation

period of battery

operation

VDD

Vlow

mgr887

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