LAPIS Semiconductor ML610472, User Manual

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ML610471/472/473/Q471/Q472/Q473 User's Manual
Chapter 7 Time Base Counter
7-9
7.3.3 Low-Speed Time Base Counter Frequency Adjustment Function
Frequency adjustment (Adjustment range: Approx. -488ppm to +488ppm. Adjustment accuracy: Approx. 0.48ppm) is
possible for outputs of T8KHZ to T1HZ of LTBC by using the low-speed time base counter frequency adjust registers
(LTBADJH and LTBADJL).
Table7-1 shows correspondence between the frequency adjustment values (LTBADJH, LTBADJL) and adjustment ratio.
Table 7-1 Correspondence between Frequency Adjustment Values (LTBADJH, LTBADJL) and Adjustment Ratio
LADJ10-0
Hexadeci
mal
Frequency
adjustment ratio
(ppm)
0 1 1 1 1 1 1 1 1 1 1 3FFH +487.80
0 1 1 1 1 1 1 1 1 1 0 3FEH +487.33
: : : : : : : : : : : :
0 0 0 0 0 0 0 0 0 1 1 003H +1.43
0 0 0 0 0 0 0 0 0 1 0 002H +0.95
0 0 0 0 0 0 0 0 0 0 1 001H +0.48
0 0 0 0 0 0 0 0 0 0 0 000H 0
1 1 1 1 1 1 1 1 1 1 1 7FFH -0.48
1 1 1 1 1 1 1 1 1 1 0 7FEH -0.95
: : : : : : : : : : : :
1 0 0 0 0 0 0 0 0 0 1 401H -487.80
1 0 0 0 0 0 0 0 0 0 0 400H -488.28
The adjustment values (LADJ10 to LADJ0) to be set in LTBADJH and LTBADJL can be obtained by using the
following equations:
Adjustment value = Frequency adjustment ratio x 2097152 (decimal)
= Frequency adjustment ratio x 200000h (hexadecimal)
Example 1: When adj15.0ppm (when the clock loses)
Adjustment value = +15.0ppm x 2097152 (decimal)
= +15.0×10
-6
×2097152
= +31.45728 (decimal)
≅
01Fh (hexadecimal)
Example 2: When adjusting
−
25.5ppm (when the clock gains)
Adjustment value =
−
25.5ppm x 2097152 (decimal)
=
−
25.5×10-6×2097152
=
−
53.477376 (decimal)
≅
7CCh (hexadecimal)
Note:
The low-speed clock (LSCLK) and the outputs of T32KHZ and T16KHZ of LTBC are not adjusted by the frequency
adjust function.
The frequency adjustment accuracy does not guarantee the accuracy including the frequency variation of the crystal
oscillation (32.768kHz) due to temperature variations.