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参数资料
| 型号： | M48T201Y-70MH6 |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 时钟/数据恢复及定时提取 |
| 英文描述： | 1 TIMER(S), REAL TIME CLOCK, PDSO44 |
| 封装： | SNAPHAT, PLASTIC, SOH-44 |
| 文件页数： | 16/32页 |
| 文件大小： | 448K |
| 代理商： | M48T201Y-70MH6 |
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M48T201Y, M48T201V
Calibrating the Clock
The M48T201Y/V is driven by a quartz controlled
oscillator with a nominal frequency of 32,768Hz.
The devices are factory calibrated at 25°C and
tested for accuracy. Clock accuracy will not ex-
ceed ±35 PPM (parts per million) oscillator fre-
quency error at 25°C, which equates to about
±1.53 minutes per month. When the Calibration
circuit is properly employed, accuracy improves to
better than +1/–2 PPM at 25°C.
The oscillation rate of crystals changes with tem-
perature
(see
The
M48T201Y/V design employs periodic counter
correction. The calibration circuit adds or subtracts
counts from the oscillator divider circuit at the di-
vide by 256 stage, as shown in Figure 14, page 25.
The number of times pulses which are blanked
(subtracted, negative calibration) or split (added,
positive calibration) depends upon the value load-
ed into the five Calibration bits found in the Control
Register. Adding counts speeds the clock up, sub-
tracting counts slows the clock down.
The Calibration bits occupy the five lower order
bits (D4-D0) in the Control Register 7FFF8h.
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 32,768Hz, 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 M48T201Y/V may re-
quire. The first involves setting the clock, letting it
run for a month and comparing it to a known accu-
rate reference and recording deviation over a fixed
period of time. Calibration values, including the
number of seconds lost or gained in a given peri-
od, can be found in the STMicroelectronics Appli-
cation
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.
The second approach is better suited to a manu-
facturing environment, and involves the use of the
IRQ/FT pin. The pin will toggle at 512Hz, when the
Stop Bit (ST, D7 of 7FFF9h) is '0,' the Frequency
Test Bit (FT, D6 of 7FFFCh) is '1,' the Alarm Flag
Enable Bit (AFE, D7 of 7FFF6h) is '0,' and the
Watchdog Steering Bit (WDS, D7 of 7FFF7h) is '1'
or the Watchdog Register (7FFF7h=0) is reset.
Note: A 4-second settling time must be allowed
before reading the 512Hz output.
Any deviation from 512Hz indicates the degree
and direction of oscillator frequency shift at the test
temperature.
For
example,
a
reading
of
512.010124Hz would indicate a +20 PPM oscilla-
tor frequency error, requiring a –10 (WR001010)
to be loaded into the Calibration Byte for correc-
tion. Note that setting or changing the Calibration
Byte does not affect the Frequency Test output
frequency.
The IRQ/FT pin is an open drain output which re-
quires a pull-up resistor to VCC for proper opera-
tion. A 500-10k
resistor is recommended in order
to control the rise time. The FT Bit is cleared on
power-down.
相关PDF资料 |
PDF描述 |
|---|---|
| M48T201Y-70MHTR | 1 TIMER(S), REAL TIME CLOCK, PDSO44 |
| M48T212V-70MH1 | 0 TIMER(S), REAL TIME CLOCK, PDSO44 |
| M48T212V-70MH6TR | 0 TIMER(S), REAL TIME CLOCK, PDSO44 |
| M48T212V-70MH6 | 0 TIMER(S), REAL TIME CLOCK, PDSO44 |
| M48T212V-70MH1TR | 0 TIMER(S), REAL TIME CLOCK, PDSO44 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| M48T201Y-80MH1 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5.0 or 3.3 V TIMEKEEPER? supervisor |
| M48T201Y-80MH1E | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5.0 or 3.3 V TIMEKEEPER? supervisor |
| M48T201Y-80MH1F | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5.0 or 3.3 V TIMEKEEPER? supervisor |
| M48T201Y-80MH1TR | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5.0 or 3.3 V TIMEKEEPER? supervisor |
| M48T201Y-85MH1 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5.0 or 3.3V TIMEKEEPER㈢ supervisor |
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