參數(shù)資料
型號(hào)： FM3808DK
廠商： Electronic Theatre Controls, Inc.
元件分類： DRAM
英文描述： 4Kb FRAM Serial 3V Memory
中文描述： 4Kb的鐵電串行3V的記憶
文件頁(yè)數(shù)： 8/28頁(yè)
文件大小： 191K
代理商： FM3808DK
FM3808
Rev 1.1
May 2003
Page 8 of 28
32.768 kHz
crystal
Oscillator
Clock
Divider
Update
Logic
32 Hz
512 Hz
W
R
Seconds
7 bits
Minutes
7 bits
Hours
6 bits
Date
6 bits
Months
5 bits
Years
8 bits
CF
Days
3 bits
User Interface Registers
1 Hz
Figure 2. Real-Time Clock Core Block Diagram
Calibration
When the CAL bit in register 7FF0h is set to 1, the
clock enters calibration mode. Interrupts are disabled
in CAL mode. Calibration operates by applying a
digital correction to the counter based on the
frequency error. In CAL mode, the INT pin is driven
with a 512 Hz nominal square wave. Any measured
deviation from 512 Hz is converted into an error in
ppm. This error corresponds to a correction value that
must then be written by the user into the calibration
register 7FF8h. The correction factors are listed in the
Table 2.
Positive ppm errors require a negative adjustment that
removes pulses. Negative ppm errors require a
positive correction that adds pulses. Positive ppm
adjustments have the CALS bit set to 1, where as
negative ppm adjustments have CALS = 0. After
calibration, the clock will have a maximum error of
±
4.34 ppm or
±
0.19 minutes per month at the
calibrated temperature.
The calibration setting is nonvolatile and is stored in
7FF8h (bits D4-D0). This value only can be written
when the CAL bit is set to a 1. To exit calibration
mode, the user must clear the CAL bit to a 0.
When the calibration mode is entered, the user can
measure the frequency error on the INT pin. This
error expressed in ppm translates directly into
timekeeping
error.
An
adjustment corrects this error. However, the
correction is applied by adding or removing pulses on
a periodic basis. Therefore, the correction will not
appear on the 512 Hz output. The calibration
correction must be applied using the values shown in
Table 2. The timekeeping accuracy can be verified by
comparing the FM3808 time to a reference source.
offsetting
calibration
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