Posted on January 06, 2007 at 14:23Hi Arul,
I tell You some informations concerning the calibration mechanism.
The calibration byte occupies the five lower order bits in the MT41T00 Control Register.
These bits represent the binary value between 0 and 31.
Each bit represents in real time for the TIMEKEEPER® product line. The sixth bit is a sign bit. A binary “1� indicates a positive calibration (added pulses), and a binary “0� indicates a negative calibration (blanked pulses).
Calibration occurs within a 64-minute cycle. The first 62 minutes in the cycle may, once per
minute, have one second either shortened by 128 or lengthened by 256 oscillator cycles. If a binary “1� is loaded into the register, only the first 2 minutes in the 64-minute cycle are modified; if a binary “6� is loaded, the first 12 are affected, and so on.
Therefore, each calibration step has the effect of adding 512 or subtracting 256 oscillator cycles for every 125,829,120 actual oscillator cycles (64 minutes x 60 seconds/minute x 32,768 cycles/second).
That is, +4.068 or –2.034 ppm of adjustment per calibration step in the calibration register. Assuming that the oscillator is running exactly at 32.768 kHz, each of the 31 increments in the calibration byte represent +10.7 or –5.35 seconds per day, which corresponds to a total range of +5.5 or –2.75 minutes per month.
I hope to be helpful.
Sixtus
