Features
a174 Direct clock/calendar replace-
ment for IBM
®
AT-compatible
computers and other applications
a174 Functionally compatible with
the DS1287/DS1287A and
MC146818A/ MC146818B
a174 242 bytes of general nonvolatile
storage
a174 Provides a 32.768kHz output for
power management
a174 System wake-up capability—
alarm interrupt active in
battery-backup mode
a174 Integral lithium cell and crystal
a174 160 ns cycle time allows fast bus
operation
a174 14 bytes for clock/calendar and
control
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 122µsto
500ms
- 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 bq3287E/bq3287EA 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 242 bytes of gen-
eral nonvolatile storage. A
32.768kHz output is available for
sustaining power-management ac-
tivities. Wake-up capability is pro-
vided by an alarm interrupt, which is
active in battery-backup mode. The
bq3287EA version is identical to the
bq3287E, with the addition of the
RAM clear input.
The bq3287E is a fully compatible
real-time clock for IBM AT-compatible
computers and other applications. The
bq3287E write-protects the clock, cal-
endar, and storage registers during
power failure. The integral backup en-
ergy source then maintains data and
operates 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 bq3287E is functionally equiva-
lent to the bq3285E, except the bat-
tery (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 is
sized to provide 10 years of data re-
tention 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 bq3285E data sheet.
1
Real-Time Clock
(
RTC
)
Module
bq3287E/bq3287EA
Sept. 1996 C
Pin Names
AD0–AD7 Multiplex address/data
input/output
MOT
CS Chip select input
AS Address strobe input
DS Data strobe input
R/W Read/write input
INT Interrupt request output
1
PN3287E1.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
EXTRAM
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
RST Reset input
SQW Square wave output
EXTRAM Extended RAM enable
NC No connect
RCL RAM clear input
(bq3287EA only)
VCC +5V supply
VSS Ground
Pin Connections