bq3287/bq3287A
Real-Time Clock (RTC) Module
Features
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Direct clock/calendar replace-
ment for IBM
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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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Integral lithium cell and crystal
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160 ns cycle time allows fast bus
operation
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Selectable Intel or Motorola 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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Time of day in seconds, minutes,
and hours
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Calendar in day of the week, day
of the month, months, and years
with automatic leap-year adjust-
ment
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Programmable square wave out-
put
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Three individually maskable in-
terrupt event flags:
bq3287A version is identical to the
bq3287, with the addition of the RAM
clear input.
The bq3287 is a fully compatible
r e a l - t i m e c l o c k f o r I B M AT-
compatible computers and other ap-
p l i c a t i o n s. T h e b q 3 2 8 7 w r i t e -
protects the clock, calendar, and
storage registers during power fail-
ure. The integral backup energy
source then maintains data and op-
erates the clock and calendar.
As shipped from Benchmarq, the
real time clock is turned off to maxi-
mize battery capacity for in-system
operation.
The bq3287 is functionally equiva-
lent to the bq3285, except that the
battery (16, 20) and crystal (2, 3)
pins are not accessible. These pins
are connected internally to a coin
cell and quartz crystal. The coin cell
is sized to provide 10 years of data
retention and clock operation in the
absence of power. For a complete de-
scription of features, operating con-
ditions, electrical characteristics,
bus timing, and pin descriptions, see
the bq3285 data sheet.
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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 bq3287/bq3287A is a
low-power microprocessor periph-
eral providing a time-of-day clock
and 100-year calendar with alarm
features and battery operation.
Ot he r fe ature s i ncl ude t hree
maskable interrupt sources, square-
wave output, and 114 bytes of gen-
e ral no n volatile storage. The
-
-
12- or 24-hour format
Optional daylight saving
adjustment
Pin Connections
MOT
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
NC
NC/RCL
NC
INT
RST
DS
NC
R/W
AS
CS
Pin Names
AD
0
鈥揂D
7
Multiplexed address/data
input/output
Bus type select input
Chip select input
Address strobe input
Data strobe input
Read/write input
Interrupt request output
RST
SQW
NC
RCL
Reset input
Square wave output
No connect
RAM clear input
(bq3287A only)
+5V supply
Ground
MOT
CS
AS
DS
R/W
INT
V
CC
V
SS
24-Pin DIP Module
PN328701.eps
Sept. 1996 D
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