RV-4162 Datasheet, PDF (17/39 Pages) MICORO CRYSTAL SWITZERLAND – Ultra Small Real Time Clock

Micro Crystal
Ultra Small Real Time Clock / Calendar Module
RV-4162
4.2. FREQUENCY OFFSET COMPENSATION
The frequency offset compensation function gives the end user the ability to calibrate the clock and to improve the
time accuracy of the RV-4162.
The RTC is clocked by an oscillator operating a quartz crystal resonator with a nominal frequency of 32.768 kHz.
The oscillator frequency on all devices is laser-trimmed and tested not to exceed a time deviation of ±20 ppm at
25°C, which equates to about ±52 seconds per month.
The RV-4162 employs periodic clock counter correction. By properly setting the frequency calibration register in the
application, it can improve its time accuracy to typically ±2 ppm at 25 °C. The frequency compensation is made by
adding or subtracting clock correction counts from the oscillator divider chain at 128 Hz (“divide by 256 stage”),
thereby changing the period of a single second.
The number of clock pulses which are subtracted (negative calibration) or added (positive calibration) depends
upon the value loaded into the five compensation bits (bit 0 to bit 4) of the Frequency Compensation Register.
Adding counts speeds the clock up; subtracting counts slows the clock down.
The frequency offset compensation is controlled by the Frequency Compensation Register 08h. The calibration
value occupies the five LSB’s (bit 4 - 0). These bits can be set to represent any value between 0 and 31 in binary
format. Bit 5 “Mode” is a sign bit; “1” indicates positive calibration and speeds up the time, “0” indicates negative
calibration and slows down the time
Freq. Compensation (address 08h…bits description)
Address
Function
Bit 7
Bit 6
08h
Calibration Register
OUT
0
Bit 5
Mode
Bit 4
16
Bit 3
8
Bit 2
4
Bit 1
2
Bit 0
1
Bit
5
4 to 0
Bit 5
0
0
0
0
0
1
1
1
1
Symbol
Mode
Calibration value
Bit 4 Bit 3 Bit 2
1
1
1
1
1
1
:
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
:
0
0
0
0
0
0
Bit 1
1
1
1
0
0
1
1
0
0
Value
0
1
0 to 31
Description
Negative calibration; compensates time deviation when 32.768 kHz clock is
too fast
Positive calibration; compensates time deviation when 32.768kHz clock is too
slow
This register holds the calibration value coded in binary format
Bit 0
1
0
0
1
0
1
0
1
0
Compensation
Value in
Decimal
+31
+30
:
+2
+1
0¹⁾
-1
-2
:
-30
-31
Frequency Compensation Event
Time correction
[ppm]
-63.054
Compensation event
1^st- 62^nd minute, 1 event each minute
-61.02
1^st - 60^th minute, 1 event each minute
:
-4.068
-2.034
1^st - 4^th minute, 1 event each minute
1^st & 2^nd minute, 1 event each minute
0
+4.068
No correction
1^st & 2^nd minute, 1 event each minute
+8.138
1^st  4^th minute, 1 event each minute
:
+122.04
+126.108
1^st - 60^th minute, 1 event each minute
1^st- 62^nd minute, 1 event each minute
1) _{Default mode at power-up.}
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