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參數(shù)資料
| 型號： | FM3808DK |
| 廠商： | Electronic Theatre Controls, Inc. |
| 元件分類： | DRAM |
| 英文描述： | 4Kb FRAM Serial 3V Memory |
| 中文描述： | 4Kb的鐵電串行3V的記憶 |
| 文件頁數(shù)： | 7/28頁 |
| 文件大?。?/td> | 191K |
| 代理商： | FM3808DK |
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FM3808
Rev 1.1
May 2003
Page 7 of 28
Real-Time Clock Operation
The real-time clock (RTC) consists of an oscillator, a
clock divider, and a register system to access the
information. It divides down the 32.768 kHz time-
base to provide the user timekeeping resolution of
one second (1Hz).
The RTC will not run until the
oscillator is enabled. The ocillator enable bit is bit 7
of register 7FF8h and is automatically set to a one
(disabled) when the device powers up without a
backup supply.
Static registers provide the user with read/write
access to the time values. The synchronization of
these registers with the timekeeper core is performed
using R and W bits in register 7FF0h. Setting the R
bit from 0 to 1 causes a transfer of the timekeeping
information to holding registers that can be read by
the user. If a timekeeper update is in progress when
the R is set, the update will be completed prior to
loading the registers. Another update cannot be
performed unless the R bit is first cleared to 0 again.
Setting the W bit causes the timekeeper to freeze
updates. Clearing it to 0 causes the values in the time
registers to be written into the timekeeper core. Users
should be sure not to load invalid values, such as FFh
to any of the timekeeping registers.
Updates to the timekeeping core occur continuously
except when frozen. A diagram of the timekeeping
core is shown below.
Backup Power
The real-time clock/calendar is intended for
permanently powered operation. When primary
system power fails, the V
DD
voltage will drop. When
it crosses the voltage on the V
BAK
supply pin, the
clock/calendar power will switch to the backup power
supply V
BAK
. The supervisor function, described
below, controls the switchover process as part of a
more complete power management circuit.
The clock uses very little current, which maximizes
battery life. Although a backup battery may be used
with the FM3808, the key advantage to combining a
clock function with FRAM is that the configuration
data (shaded regsiter bits in Table 2) is nonvolatile
and does not require a battery backup power source.
Therefore, it is more practical to use a capacitor as a
backup energy source than a battery-backed
RAM/clock combo. With the FM3808, the user has
the choice of using a battery or a capacitor as the
backup source. Some of the considerations in the
backup source decision include: The expected
duration of power outages, the difficulty of resetting
the time if lost, and the cost tradeoff of using a small
battery versus a capacitor.
The following functions are powered from the backup
power source when V
DD
< V
BAK
(backup mode) :
Clock/calendar core
Alarm interrupt/comparator
INT pin (determined by ABE & AIE bits);
active low only
Flags connected to related functions
The following functions are not powered and are
disabled when V
DD
< V
LO
:
User interface
Watchdog timer
Power monitor & band-gap (V
DD
<
≈
2.0V)
Flags connected to related functions
All FRAM access & updates
Calibration operation
INT pin if programmed as active-high
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