bq4287
Real-Time Clock Module With NVRAM Control
Features
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Direct clock/calendar replace-
ment for IBM廬
AT-compatible computers and
other applications
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Functionally compatible with the
DS1287/DS1287A and
MC146818A
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114 bytes of general nonvolatile
storage
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Automatic backup supply and
write-protection to make external
SRAM nonvolatile
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Integral lithium cell and crystal
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160 ns cycle time allows fast bus
operation
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Intel bus timing
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14 bytes for clock/calendar and
control
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BCD or binary format for clock
and calendar data
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Calendar in day of the week, day of
the month, months, and years with
automatic leap-year adjustment
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Time of day in seconds, minutes,
and hours
114 bytes of general nonvolatile
storage.
The bq4287 write-protects the clock,
calendar, and storage registers dur-
ing power failure. The integral
backup energy source then main-
tains data and operates the clock
and calendar.
The bq4287 uses its integral battery-
backup controller and battery to make
a standard CMOS SRAM nonvolatile
during power-fail conditions. During
power-fail, the bq4287 automatically
write-protects the external SRAM and
provides a V
CC
output sourced from its
internal battery.
The bq4287 is a fully compatible
real-time clock for IBM AT-compatible
computers and other applications.
As shipped from Benchmarq, the
backup cell is electrically isolated
from the memory. Following the first
application of V
CC
, this isolation is
broken, and the backup cell provides
data retention to the clock, internal
RAM, V
OUT
, and CE
OUT
on subse-
quent power-downs.
The bq4287 is functionally equiva-
lent to the bq4285, except that the
battery (16, 20) and crystal pins (2,
3) are not accessible. These pins are
connected internally to a coin cell
and quartz crystal. The coin cell pro-
vides 130mAh of capacity. For a
complete description of features, op-
erating conditions, electrical charac-
teristics, bus timing, and pin de-
scriptions, see the bq4285 data
sheet.
Caution:
Take care to avoid inadvertent dis-
charge through V
OUT
and CE
OUT
after battery isolation has been
broken.
-
-
12- or 24-hour format
Optional daylight saving
adjustment
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Programmable square wave out-
put
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Three individually maskable in-
terrupt event flags:
-
-
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Periodic rates from 122
碌s
to
500 ms
Time-of-day alarm once per
second to once per day
End-of-clock update cycle
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Better than one minute per
month clock accuracy
General Description
The CMOS bq4287 is a low-power
microprocessor peripheral providing
a time-of-day clock and 100-year cal-
endar with alarm features and bat-
tery operation. Other features in-
clude three maskable interrupt
sources, square wave output, and
Pin Connections
Pin Names
AD
0
鈥揂D
7
Multiplexed address/data
input/output
Chip select input
Address strobe input
Data strobe input
Read/write input
Interrupt request output
Reset input
Square wave output
RAM chip enable input
RAM chip enable output
No connect
Supply output
+5V supply
Ground
CS
ALE
RD
WR
INT
RST
SQW
CE
IN
CE
OUT
NC
V
OUT
V
CC
V
SS
VOUT
NC
NC
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
VSS
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
VCC
SQW
CEOUT
CEIN
NC
INT
RST
RD
NC
WR
ALE
CS
24-Pin DIP Module
PN428701.eps
Nov. 1993 C
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