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参数资料
| 型号： | M41ST85YMH6F |
| 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, SNAPHAT, LEAD FREE, PLASTIC, SOH-28 |
| 文件页数： | 7/34页 |
| 文件大小： | 532K |
| 代理商： | M41ST85YMH6F |
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M41ST85Y, M41ST85W
Calibrating the Clock
The M41ST85Y/W is driven by a quartz controlled
oscillator with a nominal frequency of 32,768 Hz.
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 16). Therefore, the
M41ST85Y/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 16. 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 32,768 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 M41ST85Y/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, “TIMEKEEP-
ER CALIBRATION.” This allows the designer to
give the end user the ability to calibrate the clock
as the environment requires, even if the final prod-
uct is packaged in a non-user serviceable enclo-
sure. 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/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 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 oscilla-
tor 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 to10k 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 |
|---|---|
| M41ST85YMH6E | 1 TIMER(S), REAL TIME CLOCK, PDSO28 |
| M41T11MH6 | 0 TIMER(S), REAL TIME CLOCK, PDSO28 |
| M41T11M6 | 0 TIMER(S), REAL TIME CLOCK, PDSO8 |
| M41T11MH6TR | 0 TIMER(S), REAL TIME CLOCK, PDSO28 |
| M41T56M6E | 0 TIMER(S), REAL TIME CLOCK, PDSO8 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| M41ST85YMH6TR | 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 and NVRAM SUPERVISOR |
| M41ST85YMX | 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 and NVRAM SUPERVISOR |
| M41ST85YMX6 | 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 |
| M41ST85YMX6TR | 制造商:STMicroelectronics 功能描述:REAL TIME CLOCK SERL 64BYTE 28PIN SOX - Tape and Reel |
| M41ST85YSH | 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 and NVRAM SUPERVISOR |
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