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参数资料
| 型号： | M41ST84YMH6E |
| 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, PDSO28 |
| 封装： | 0.330 INCH, LEAD FREE, PLASTIC, SOH-28 |
| 文件页数： | 6/31页 |
| 文件大小： | 507K |
| 代理商： | M41ST84YMH6E |
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M41ST84Y, M41ST84W
14/31
Calibrating the Clock
The M41ST84Y/W is driven by a quartz controlled
oscillator with a nominal frequency of 32,768Hz.
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 ±2 ppm
at 25°C.
The oscillation rate of crystals changes with tem-
perature (see Figure 15., page 15). Therefore, the
M41ST84Y/W 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
16., 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 (08h). 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 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 M41ST84Y/W may re-
quire.
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.
The second approach is better suited to a manu-
facturing environment, and involves the use of the
IRQ/FT/OUT pin. The pin will toggle at 512Hz,
when the Stop Bit (ST, D7 of 01h) is '0,' the Fre-
quency Test Bit (FT, D6 of 08h) is '1,' the Alarm
Flag Enable Bit (AFE, D7 of 0Ah) is '0,' and the
Watchdog Steering Bit (WDS, D7 of 09h) is '1' or
the Watchdog Register (09h = 0) is reset.
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 (XX001010) 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/OUT pin is an open drain output
which requires a pull-up resistor to VCC for proper
operation. A 500 to 10k resistor is recommended
in order to control the rise time. The FT Bit is
cleared on power-down.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| M41ST84YMQ | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5.0 or 3.0V, 512 bit 64 x 8 SERIAL RTC with SUPERVISORY FUNCTIONS |
| M41ST84YMQ1 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5.0 or 3.0V, 512 bit 64 x 8 SERIAL RTC with SUPERVISORY FUNCTIONS |
| M41ST84YMQ1TR | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5.0 or 3.0V, 512 bit 64 x 8 SERIAL RTC with SUPERVISORY FUNCTIONS |
| M41ST84YMQ6 | 功能描述:实时时钟 Serial 512 (64x8) RoHS:否 制造商:Microchip Technology 功能:Clock, Calendar. Alarm RTC 总线接口:I2C 日期格式:DW:DM:M:Y 时间格式:HH:MM:SS RTC 存储容量:64 B 电源电压-最大:5.5 V 电源电压-最小:1.8 V 最大工作温度:+ 85 C 最小工作温度: 安装风格:Through Hole 封装 / 箱体:PDIP-8 封装:Tube |
| M41ST84YMQ6E | 功能描述:IC RTC 5.0V 512BIT NVRAM 16SOIC RoHS:否 类别:集成电路 (IC) >> 时钟/计时 - 实时时钟 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:1 系列:- 类型:时钟/日历 特点:警报器，闰年，SRAM 存储容量:- 时间格式:HH:MM:SS（12/24 小时） 数据格式:YY-MM-DD-dd 接口:SPI 电源电压:2 V ~ 5.5 V 电压 - 电源，电池:- 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-WDFN 裸露焊盘 供应商设备封装:8-TDFN EP 包装:管件 |
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