78M6612 Data Sheet
DS_6612_001
32768.5
32768.4
32768.3
32768.2
32768.1
32768
32767.9
32767.8
32767.7
32767.6
32767.5
crystal
curve fit
inverse curve
-50
-25
0
25
50
Figure 30: Crystal Compensation
The MPU Demo Code supplied with the Teridian Demo Kits has a direct interface for these coefficients
and it directly controls the RTC_DEC_SEC or RTC_INC_SEC registers. The Demo Code uses the
coefficients in the form:
Y _ CAL
Y _ CALC
Y _ CALC2
CORRECTION(ppm) =
+T ⋅
+T 2 ⋅
10
100
1000
Note that the coefficients are scaled by 10, 100, and 1000 to provide more resolution. For our example
case, the coefficients would then become (after rounding):
Y_CAL = 109, Y_CALC = 12, Y_CALC2 = 7
Alternatively, the mains frequency may be used to stabilize or check the function of the RTC. For this
purpose, the CE provides a count of the zero crossings detected for the selected line voltage in the
MAIN_EDGE_X address. This count is equivalent to twice the line frequency, and can be used to
synchronize and/or correct the RTC.
3.5 Connecting 5V Devices
All digital input pins of the 78M6612 are compatible with external 5V devices. I/O pins configured as
inputs do not require current-limiting resistors when they are connected to external 5V devices.
66
Rev. 1.2
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
