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| 型号： | M48T212V-85MH1E |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 时钟/数据恢复及定时提取 |
| 英文描述： | REAL TIME CLOCK, PDSO44 |
| 封装： | 0.330 INCH, ROHS COMPLIANT, PLASTIC, SOH-44 |
| 文件页数： | 16/35页 |
| 文件大小： | 348K |
| 代理商： | M48T212V-85MH1E |
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M48T212V
Clock operation
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 calibration 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 M48T212Y/V may
require. The first involves setting the clock, letting it run for a month and comparing it to a
known accurate reference 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 accesses the Calibration byte.
The second approach is better suited to a manufacturing environment, and involves the use
of the IRQ/FT pin. The pin will toggle at 512Hz, when the Stop Bit (ST, D7 of 9h) is '0,' the
Frequency Test Bit (FT, D6 of Ch) is '1,' the Alarm Flag Enable Bit (AFE, D7 of 6h) is '0,' and
the Watchdog Steering Bit (WDS, D7 of 7h) is '1' or the Watchdog Register (7h=0) is reset.
Any deviation from 512 Hz indicates the degree and direction of oscillator frequency shift at
the test temperature. For example, a reading of 512.010124 Hz 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 frequency.
The IRQ/FT pin is an open drain output which requires a pull-up resistor to VCC for proper
operation. A 500-10k
Ω resistor is recommended in order to control the rise time. The FT Bit
is cleared on power-up.
3.11
Battery low warning
The M48T212V automatically performs battery voltage monitoring upon power-up and at
factory-programmed time intervals of approximately 24 hours. The Battery Low (BL) Bit, Bit
D4 of Flags Register 0h, will be asserted if the battery voltage is found to be less than
approximately 2.5V. The BL Bit will remain asserted until completion of battery replacement
and subsequent battery low monitoring tests, either during the next power-up sequence or
the next scheduled 24-hour interval.
If a battery low is generated during a power-up sequence, this indicates that the battery is
below approximately 2.5 volts and may not be able to maintain data integrity in the SRAM.
Data should be considered suspect and verified as correct. A fresh battery should be
installed.
If a battery low indication is generated during the 24-hour interval check, this indicates that
the battery is near end of life. However, data is not compromised due to the fact that a
nominal VCC is supplied. In order to ensure data integrity during subsequent periods of
battery back-up mode, the battery should be replaced. The SNAPHAT battery/crystal top
should be replaced with VCC powering the device to avoid data loss.
Note:
This will cause the clock to lose time during the time interval the battery crystal is removed.
The M48T212V only monitors the battery when a nominal VCC is applied to the device. Thus
applications which require extensive durations in the battery back-up mode should be
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相关代理商/技术参数 |
参数描述 |
|---|---|
| M48T212V-85MH1F | 功能描述:监控电路 SRAM TK 16X8 85ns RoHS:否 制造商:STMicroelectronics 监测电压数: 监测电压: 欠电压阈值: 过电压阈值: 输出类型:Active Low, Open Drain 人工复位:Resettable 监视器:No Watchdog 电池备用开关:No Backup 上电复位延迟（典型值）:10 s 电源电压-最大:5.5 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:UDFN-6 封装:Reel |
| M48T212V-85MH1TR | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5V/3.3V TIMEKEEPER[ CONTROLLER |
| M48T212V-85MH6 | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5V/3.3V TIMEKEEPER[ CONTROLLER |
| M48T212V-85MH6E | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5V/3.3V TIMEKEEPER CONTROLLER Supervisor |
| M48T212V-85MH6F | 制造商:STMICROELECTRONICS 制造商全称:STMicroelectronics 功能描述:5V/3.3V TIMEKEEPER CONTROLLER Supervisor |
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