參數(shù)資料
型號(hào)： M48T559YMH1F
廠商： STMICROELECTRONICS
元件分類： 時(shí)鐘/數(shù)據(jù)恢復(fù)及定時(shí)提取
英文描述： REAL TIME CLOCK, PDSO28
封裝： 0.330 INCH, LEAD FREE, PLASTIC, SOH-28
文件頁(yè)數(shù)： 4/26頁(yè)
文件大?。?/td> 364K
代理商： M48T559YMH1F
M48T559Y
12/26
Figure 8. Back-Up Mode Alarm Waveform
Calibrating the Clock
The M48T559Y is driven by a quartz controlled os-
cillator with a nominal frequency of 32,768 Hz. The
devices are tested not exceed +/–35 ppm (parts
per million) oscillator frequency error at 25oC,
which equates to about +/–1.53 minutes per
month. When the Calibration circuit is properly em-
ployed, accuracy improves to better than +1/–2
ppm at 25°C.
The oscillation rate of crystals changes with tem-
perature (see Figure 10., page 15). Therefore, the
M48T559Y design employs periodic counter cor-
rection. The calibration circuit adds or subtracts
counts from the oscillator divider circuit at the di-
vide
by
256
stage,
as
shown
in
11., page 15. The number of times pulses which
are blanked (subtracted, negative calibration) or
split (added, positive calibration) depends upon
the value loaded into the five Calibration Bits found
in the Control Register. Adding counts speeds the
clock up, subtracting counts slows the clock down.
The Calibration Bits occupy the five lower order
bits (D4-D0) in the Control Register (1FF8h).
These bits can be set to represent any value be-
tween 0 and 31 in binary form. Bit D5 is a Sign Bit;
'1' indicates positive calibration, '0' indicates nega-
tive calibration. 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 will
be modified; if a binary 6 is loaded, the first 12 will
be 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, that is
+4.068 or –2.034 ppm of adjustment per calibra-
tion step in the calibration register. Assuming that
the oscillator is running at exactly 32,768 Hz, each
of the 31 increments in the Calibration byte would
represent +10.7 or –5.35 seconds per month
which corresponds to a total range of +5.5 or –2.75
minutes per month.
Two methods are available for ascertaining how
much calibration a given M48T559Y may require:
The first involves setting the clock, letting it run for
a month and comparing it to a known accurate ref-
erence and recording deviation over a fixed period
of time. Calibration values, including the number of
seconds lost or gained in a given period, can be
found in Application Note AN934: TIMEKEEPER
CALIBRATION. This allows the designer to give
the end user the ability to calibrate the clock as the
environment requires, even if the final product is
packaged in a non-user serviceable enclosure.
The designer could provide a simple utility that ac-
cesses the Calibration byte.
AI01678C
VCC
IRQ/FT
HIGH-Z
VPFD (max)
VPFD (min)
ABE, AFE bits in Interrupt Register
AF bit in Flags Register
HIGH-Z
VSO
trec
相關(guān)PDF資料
PDF描述
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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M48T58 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:5.0V, 64 Kbit (8 Kb x 8) TIMEKEEPER SRAM
M48T58_07 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:5.0V, 64 Kbit (8 Kb x 8) TIMEKEEPER SRAM
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