PCF2123 Datasheet, PDF (29/54 Pages) NXP Semiconductors – SPI Real time clock/calendar

NXP Semiconductors
PCF2123
SPI Real time clock/calendar
Table 36. Register Offset_register
OFFSET[6:0]
Offset value in
decimal
0 1 1 1 1 1 1 +63
0 1 1 1 1 1 0 +62
:
:
0 0 0 0 0 1 0 +2
0 0 0 0 0 0 1 +1
0 0 0 0 0 0 0 0^[1]
1 1 1 1 1 1 1 −1
1 1 1 1 1 1 0 −2
:
:
1 0 0 0 0 0 1 −63
1 0 0 0 0 0 0 −64
[1] Default mode.
Offset value in ppm
Normal mode
MODE = 0
+136.71
+134.54
:
+4.34
+2.17
0
−2.17
−4.34
:
−136.71
−138.88
Course mode
MODE = 1
+273.42
+269.08
:
+8.68
+4.34
0
−4.34
−8.68
:
−273.42
−277.76
The correction is made by adding or subtracting 64 Hz clock correction pulses, thereby
changing the period of a single second.
Table 37. Example of converting the offset in ppm to seconds
Offset in ppm Seconds per
Day
Week
Month
2.17
0.187
1.31
5.69
4.34
0.375
2.62
11.4
Year
68.2
136
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).
PCF2123_1
Product data sheet
Rev. 01 — 19 November 2008
© NXP B.V. 2008. All rights reserved.
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