PT7C4372A Datasheet, PDF (14/30 Pages) Pericom Semiconductor Corporation – Real-time Clock Module

PT7C4372A/4372C
Real-time Clock Module (I²C Bus)
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Clock Precision Adjustment Function
Adjustment range
Adjustment range (ppm)
Adjustment unit (ppm)
Internal timing of adjustment
-189.1 to +189.1
3.05 ^*
Once every 20 seconds at “00”, “20”, “40” seconds
* _{note: add or decrement 2 clock pulses every 20s: 2/(32,76820) = 3.051ppm (or 3.125ppm when 32.000kHz crystal is used).}
Adjustment amount and adjustment value
Adjustment amount
(ppm)
Adjustment data
Decimal
Hexadecimal
-189.10
-186.05
-183.00
+63
3F h
+62
3E h
+61
3D h
bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
F6 F5 F4 F3 F2 F1 F0
0
1
1
1
1
1
1
0
1
1
1
1
1
0
0
1
1
1
1
0
1
-9.15
-6.10
-3.05
OFF
OFF
+3.05
+6.10
+9.15
+4
04 h
0
0
0
0
1
0
0
+3
03 h
0
0
0
0
0
1
1
+2
02 h
0
0
0
0
0
1
0
+1
01 h
0
0
0
0
0
0
1
0
00 h
0
0
0
0
0
0
0
-1
7F h
1
1
1
1
1
1
1
-2
7E h
1
1
1
1
1
1
0
-3
7D h
1
1
1
1
1
0
1
+183.00
+186.05
+189.10
OFF
OFF
-60
44 h
1
0
0
0
1
0
0
-61
43 h
1
0
0
0
0
1
1
-62
42 h
1
0
0
0
0
1
0
-63
41 h
1
0
0
0
0
0
1
-64
40 h
1
0
0
0
0
0
0
Examples:
(1) Setting time forward
Adjust (advance) the clock precision when FOUT clock output is 32767.7 Hz
Determine the current amount of variance
(32767.7 -32768) / 32768 = -9.16 ×10 ^-6
*[ 32768 ] = Reference values
Calculate the optimum adjustment data (decimal value) relative to the current variance.
Adjustment data = variance / adjustment resolution = -9.16 / 3.05  -3
Calculate the setting adjustment data (hexadecimal)
Setting adjustment data = 128 -3 (80 h – 03h) = 125 (7D h)
(2) Setting time backward
Adjust (set back) the clock precision when FOUT clock output is 32768.3 Hz
Determine the current amount of variance
(32768.3 -32768) / 32768 = +9.16 ×10 ^-6
Calculate the optimum adjustment data (decimal value) relative to the current variance.
Adjustment data = (variance / adjustment resolution) + 1 = (+9.16 / 3.05) + 1  +4
*Add 1 since reference value is 01h
Calculate the setting adjustment data (hexadecimal)
Setting adjustment data = 04 h
12-07-0001
PT0150-8 07/04/12
14