PCF2123TS datasheet(28/55 Pages) NXP

28 / 55 page

PCF2123_2

Product data sheet

Rev. 02 — 4 December 2009

28 of 55

NXP Semiconductors

PCF2123

SPI Real time clock/calendar

[1]

Default mode.

The correction is made by adding or subtracting 64 Hz clock correction pulses, thereby

changing the period of a single second.

In normal mode, the correction is triggered once per two hours and then correction pulses

are applied once per minute until the programmed correction values has been implement.

In course mode, the correction is triggered once per hour and then correction pulses are

applied once per minute up to a maximum of 60 minutes. When correction values greater

than 60 are used, additional correction pulses are made in the 59th minute (see Table 38).

Table 36.

OFFSET[6:0]

Offset value in

decimal

Offset value in ppm

Normal mode

MODE = 0

Course mode

MODE = 1

0 1 1 1 1 1 1

+63

+136.71

+273.42

0 1 1 1 1 1 0

+62

+134.54

+269.08

:::

0 0 0 0 0 1 0

+4.34

+8.68

0 0 0 0 0 0 1

+2.17

+4.34

0000000

0[1]

1111111

−1

−2.17

−4.34

1111110

−2

−4.34

−8.68

:::

1000001

−63

−136.71

−273.42

1000000

−64

−138.88

−277.76

Table 37.

Example of converting the offset in ppm to seconds

Offset in ppm

Seconds per

Day

Week

Month

Year

2.17

0.187

1.31

5.69

68.2

4.34

0.375

2.62

11.4

136

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