Data Sheet

SD2405ALPI IIC 串行接口的实时时钟IC
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*1) Oscillation frequency: Clock frequency output from the INT pin
*2) Target frequency: TYP. 32.768KHz to 32.000KHz
*3) Adjustment amount: A value to be set finally to F6 to F0 bits. This value is
expressed in 7 bit binary digits with sign bit (two’s compliment).
2. When oscillation frequency = target frequency (no clock gain or loss)
Set the adjustment value to 0 or +1, or –64, or –63 to disable adjustment.
3. When oscillation frequency < target frequency (clock losses)
Example of Calculations
1) When oscillation frequency = 32770kHz; target frequency = 32768kHz
Adjustment value = （32770-32768+0.1）/(32770*2/(32768*20))
=(32770-32768)*10+1=21
Set （F6，F5，F4，F3，F2，F1，F0）=（0，0，1，0，1，0，1）
2) When oscillation frequency =32762kHz; target frequency = 32768kHz
Adjustment value =（32762-32768）/(32762*2/(32768*20))
= (32762-32768)*10=-60
To express –60 in 7bi binary digits with sign bit ( two’s compliment)
Subtract 60(3Ch) from 128(80h) in the above case, 80h-3Ch=44h
Thus set （F6，F5，F4，F3，F2，F1，F0）=（1，0，0，0，1，0，0）
After adjustment, adjustment error against the target frequency will the approx.
±1.5ppm at a room temperature.
Notice:
1) Clock frequency output from the INT pin will change after adjustment by the clock
adjustment circuit.
2) Adjustment range:
A)When oscillation frequency is higher than target frequency, the range of adjustment
values is （F6，F5，F4，F3，F2，F1，F0）=（0，0，0，0，0，0，1）to (0，1，1 ，
1，1，1，1) and actual adjustable amount shall be -3.05ppm to –189.2ppm (-3.125ppm
to 193.7ppm for 32000Hz crystal).
B) When oscillation frequency is lower than target frequency, the range of adjustment values
is （F6，F5，F4，F3，F2，F1，F0）=（1，1，1，1，1，1，1）to（1，0，0，
0，0，1，0）and actual adjustable amount shall be 3.05ppm to 189.2ppm (3.125ppm to
193.7ppm for 32000Hz crystal).
5.5 User Registers
Addresses [14h to 1Fh]
SD2405AL provides 12 bytes of general-purpose RAM for the user to store data.
5.6 Other control / status bits