PCF8523 datasheet(27/66 Pages) NXP

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PCF8523

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Product data sheet

Rev. 3 — 30 March 2011

27 of 66

NXP Semiconductors

PCF8523

Real-Time Clock (RTC) and calendar

8.8 Register Offset

The PCF8523 incorporates an offset register (address 0Eh), which can be used to

implement several functions, like:

• Aging adjustment,

• Temperature compensation,

• Accuracy tuning.

[1]

Default value.

Each LSB will introduce an offset of 4.34 ppm for MODE = 0 and 4.069 ppm for

MODE = 1. The values of 4.34 ppm and 4.069 ppm are based on a nominal 32.768 kHz

clock. The offset value is coded in two’s complement giving a range of +63 LSB

64 LSB.

[1]

Default mode.

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

the period of a single second.

It is possible to monitor when correction pulses are applied. To enable correction interrupt

generation, bit CIE (register Control_1) has to be set logic 1. At every correction cycle a



4096 s pulse will be generated on pin INT1. In the case that multiple correction pulses are

applied, a 1



4096 s interrupt pulse will be generated for each correction pulse applied.

Table 26.

Offset - offset register (address 0Eh) bit description

Bit

Symbol

Value

Description

7MODE

0[1]

offset is made once every two hours

offset is made once every minute

6 to 0

OFFSET[6:0]

see Table 27

offset value

Table 27.

Offset values

OFFSET[6:0]

Offset value in

decimal

Offset value in ppm

Every two hours

(MODE = 0)

Every minute

(MODE = 1)

0111111

+63

+273.420

+256.347

0111110

+62

+269.080

+252.278

::::

0000010

+8.680

+8.138

0000001

+4.340

+4.069

0000000

0[1]

1111111

1

4.340

4.069

1111110

2

8.680

8.138

::::

1000001

63

273.420

256.347

1000000

64

277.760

260.416

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