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参数资料
| 型号： | M48T129Y-85PM1 |
| 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, DMA32 |
| 封装： | PLASTIC, MODULE, DIP-32 |
| 文件页数： | 7/30页 |
| 文件大小： | 483K |
| 代理商： | M48T129Y-85PM1 |
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M48T129Y, M48T129V
Calibrating the Clock
The M48T129Y/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 frequen-
cy error at 25°C, which equates to about ±1.53
minutes per month (see Figure 10., page 16).
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
temperature. The M48T129Y/V design employs
periodic counter correction. The calibration circuit
adds or subtracts counts from the oscillator divider
circuit at the divide by 256 stage, as shown in Fig-
The number of times pulses are blanked (subtract-
ed, negative calibration) or split (added, positive
calibration) depends upon the value loaded into
the five Calibration bits found in the Control Regis-
ter. Adding counts speeds the clock up, subtract-
ing counts slows the clock down. The Calibration
bits occupy the five lower order bits (D4-D0) in the
Control Register 1FFF8h. These bits can be set to
represent any value between 0 and 31 in binary
form. Bit D5 is a Sign Bit; '1' indicates positive cal-
ibration, '0' indicates negative calibration. Calibra-
tion 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 modi-
fied; if a binary 6 is loaded, the first 12 will be af-
fected, and so on. Therefore, each calibration step
has the effect of adding 512 or subtracting 256 os-
cillator cycles for every 125, 829, 120 actual oscil-
lator cycles, that is +4.068 or –2.034 ppm of
adjustment per calibration 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. Figure
tion waveform.
Two methods are available for ascertaining how
much calibration a given M48T129Y/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 sec-
onds lost or gained in a given period, can be found
in the application note “AN934, TIMEKEEPER
CALIBRATION.”
This allows the designer to give the end user the
ability to calibrate the clock as the environment re-
quires, even if the final product is packaged in a
non-user serviceable enclosure. The designer
could 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 the
IRQ/FT pin. The pin will toggle at 512Hz, when the
Stop Bit (ST, D7 of 1FFF9h) is '0,' the Frequency
Test Bit (FT, D6 of 1FFFCh) is '1,' the Alarm Flag
Enable Bit (AFE, D7 of 1FFF6h) is '0,' and the
Watchdog Steering Bit (WDS, D7 of 1FFF7h) is '1'
or the Watchdog Register (1FFF7h = 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 oscillator
frequency error, requiring a –10 (WR001010) to be
loaded into the Calibration Byte for correction.
Note that setting or changing the Calibration Byte
does not affect the Frequency test output frequen-
cy.
The IRQ/FT pin is an open drain output which re-
quires a pull-up resistor for proper operation. A
500-10k
resistor is recommended in order to
control the rise time. The FT Bit is cleared on pow-
er-up.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| M48T129YPM | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:3.3V-5V 1 Mbit 128Kb x8 TIMEKEEPER SRAM |
| M48T129YSH | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:3.3V-5V 1 Mbit 128Kb x8 TIMEKEEPER SRAM |
| M48T18 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5V, 64Kbit (8 Kb x 8) TIMEKEEPER㈢ SRAM |
| M48T18-100MH1 | 功能描述:RAM其它 8KX8 TIMEKEEP 100NS RoHS:否 制造商:Freescale Semiconductor 封装:Tray |
| M48T18-100MH1E | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:64 Kbit 8Kb x 8 TIMEKEEPER SRAM |
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