參數(shù)資料
型號: DS12B887
英文描述: Real Time Clock
中文描述: 實時時鐘
文件頁數(shù): 2/16頁
文件大小: 102K
代理商: DS12B887
DS12B887
080895 2/16
OPERATION
The block diagram in Figure 1 shows the pin connec-
tions with the major internal functions of the DS12B887.
The following paragraphs describe the function of each
pin.
BLOCK DIAGRAM DS12B887
Figure 1
USER RAM
114 BYTES
CAND ALARM RAM
REGISTERS A,B,C,D
SQUARE
WAVE OUT
PERIODIC INTERRUPT/SQUARE WAVE
SELECTOR
OSC.
POWER
SWITCH
AND
WRITE
PROTECT
BUS
INTERFACE
CLOCK/
CALENDAR
UPDATE
BCD/
BINARY
INCREMENT
SQW
IRQ
DOUBLE
BUFFERED
ADO–
AD7
AS
DS
R/W
CS
CS
V
CC
POK
V
CC
V
BAT
8
64
64
RAM
CLEAR
LOGIC
RCLR
POWER-DOWN/POWER-UP
CONSIDERATIONS
The Real Time Clock function will continue to operate
and all of the RAM, time, calendar, and alarm memory
locations remain nonvolatile regardless of the level of
the V
CC
input. When V
CC
is applied to the DS12B887
and reaches a level of greater than 4.25 volts, the device
becomes accessible after 200 ms, provided that the
oscillator is running and the oscillator countdown chain
is not in reset (see Register A). This time period allows
the system to stabilize after power is applied. When
V
CC
falls below 4.25 volts, the chip select input is inter-
nally forced to an inactive level regardless of the value of
CS at the input pin. The DS12B887 is, therefore, write-
protected. When the DS12B887 is in a write-protected
state, all inputs are ignored and all outputs are in a high
impedance state. When V
CC
falls below a level of
approximately 3 volts, the external V
CC
supply is
switched off and an internal lithium energy source sup-
plies power to the Real Time Clock and the RAM
memory.
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