Features
a174 Direct clock/calendar replace-
ment for IBM
®
AT-compatible
computers and other applications
a174 Functionally compatible with the
DS1287/DS1287A and MC146818A
a174 114 bytes of general nonvolatile
storage
a174 Integral lithium cell and crystal
a174 160 ns cycle time allows fast bus
operation
a174 Selectable Intel or Motorola bus
timing
a174 14 bytes for clock/calendar and
control
a174 BCD or binary format for clock
and calendar data
a174 Time of day in seconds, minutes,
and hours
- 12- or 24-hour format
- Optional daylight saving
adjustment
a174 Calendar in day of the week, day
of the month, months, and years
with automatic leap-year adjust-
ment
a174 Programmable square wave out-
put
a174 Three individually maskable in-
terrupt event flags:
- Periodic rates from 122 µsto
500 ms
- Time-of-day alarm once per
second to once per day
- End-of-clock update cycle
a174 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.
Other features include three
maskable interrupt sources, square-
wave output, and 114 bytes of gen-
eral nonvolatile storage. The
bq3287A version is identical to the
bq3287, with the addition of the RAM
clear input.
The bq3287 is a fully compatible
real-time clock for IBM AT-
compatible computers and other ap-
plications. The bq3287 write-
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.
1
Pin Names
AD0–AD7 Multiplexed address/data
input/output
MOT Bus type select input
CS Chip select input
AS Address strobe input
DS Data strobe input
R/W Read/write input
INT Interrupt request output
1
PN328701.eps
24-Pin DIP Module
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
9
10
16
15
11
12
14
13
V
CC
SQW
NC
NC
INT
RST
DS
NC
R/W
AS
CS
MOT
NC
NC
AD
0
AD
1
AD
2
AD
3
AD
4
AD
5
AD
6
AD
7
V
SS
NC/RCL
Sept. 1996 D
RST Reset input
SQW Square wave output
NC No connect
RCL RAM clear input
(bq3287A only)
VCC +5V supply
VSS Ground
Pin Connections
bq3287/bq3287A
Real-Time Clock
(
RTC
)
Module