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参数资料
| 型号： | M48T35-70PC6 |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 时钟/数据恢复及定时提取 |
| 英文描述： | 0 TIMER(S), REAL TIME CLOCK, PDIP28 |
| 封装： | 0.600 INCH, CAPHAT, PLASTIC, DIP-28 |
| 文件页数： | 3/18页 |
| 文件大小： | 140K |
| 代理商： | M48T35-70PC6 |
11/18
M48T35, M48T35Y
Two methods are available for ascertaining how
much calibration a given M48T35/35Y may re-
quire. The first involves simply setting the clock,
letting it run for a month and comparing it to a
known accurate reference (like WWV broadcasts).
While that may seem crude, it allows the designer
to give the end user the ability to calibrate his clock
as his environment may require, even after the fi-
nal product is packaged in a non-user serviceable
enclosure.
All the designer has to do is provide a simple utility
that accesses the Calibration byte.
The second approach is better suited to a manu-
facturing environment, and involves the use of
some test equipment. When the Frequency Test
(FT) bit, the seventh-most significant bit in the Day
Register is set to a ’1’, and D7 of the Seconds Reg-
ister is a ’0’ (Oscillator Running), DQ0 will toggle at
512Hz during a read of the Seconds Register. Any
deviation from 512 Hz indicates the degree and di-
rection of oscillator frequency shift at the test tem-
perature. For example, a reading of 512.01024 Hz
would indicate a +20 ppm oscillator frequency er-
ror, requiring a –10 (WR001010) to be loaded into
the Calibration Byte for correction. Note that set-
ting or changing the Calibration Byte does not af-
fect
the
Frequency
test
output
frequency.
The FT bit MUST be reset to '0' for normal clock
operations to resume. The FT bit is automatically
Reset on power-up.
For more information on calibration, see the Appli-
cation Note AN934 "TIMEKEEPER Calibration".
Most clock chips compensate for crystal frequency
and temperature shift error with cumbersome trim
capacitors. The M48T35/35Y design, however,
employs periodic counter correction. The calibra-
tion circuit adds or subtracts counts from the oscil-
lator divider circuit at the divide by 256 stage, as
shown in Figure 9. The number of times pulses 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 byte occupies the five lower order
bits (D4-D0) in the Control Register 7FF8h. These
bits can be set to represent any value between 0
and 31 in binary form. Bit D5 is a Sign bit; '1' indi-
cates positive calibration, '0' indicates negative
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 bi-
nary '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 in fact 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.
Figure 9. Clock Calibration
AI00594B
NORMAL
POSITIVE
CALIBRATION
NEGATIVE
CALIBRATION
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相关代理商/技术参数 |
参数描述 |
|---|---|
| M48T35-70PC6E | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5V, 256 Kbit (32 Kb x 8) TIMEKEEPER SRAM |
| M48T35-70PC6F | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5V, 256 Kbit (32 Kb x 8) TIMEKEEPER SRAM |
| M48T35-70PC6TR | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:256 Kbit 32Kb x8 TIMEKEEPER SRAM |
| M48T35-70PM1 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5V, 256 Kbit (32 Kb x 8) TIMEKEEPER SRAM |
| M48T35-70PM1E | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5V, 256 Kbit (32 Kb x 8) TIMEKEEPER SRAM |
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