Features
a174 Direct clock/calendar replace-
ment for IBM
®
AT-compatible
computers and other applications
a174 Functionally compatible with the
DS1285
- Closely matches MC146818A
pin configuration
a174 2.7–3.6V operation (bq3285L);
4.5–5.5V operation (bq3285E)
a174 242 bytes of general nonvolatile
storage
a174 32.768kHz output for power man-
agement
a174 System wake-up capability—
alarm interrupt output active in
battery-backup mode
a174 Less than 0.5µA load under bat-
tery 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 Calendar in day of the week, day
of the month, months, and years,
with automatic leap-year adjust-
ment
a174 Time of day in seconds, minutes,
and hours
- 12- or 24-hour format
- Optional daylight saving
adjustment
a174 Programmable square wave out-
put
a174 Three individually maskable in-
terrupt event flags:
- Periodic rates from 122µs to
500ms
- Time-of-day alarm once per
second to once per day
- End-of-clock update cycle
a174 24-pin plastic DIP, SOIC, or
SSOP
General Description
The CMOS bq3285E/L is a low-
power microprocessor peripheral
providing a time-of-day clock and
100-year calendar with alarm fea-
tures and battery operation. The
bq3285L supports 3V systems.
Other bq3285E/L features include
three maskable interrupt sources,
square-wave output, and 242 bytes
of general 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.
Thebq3285E/Lwrite-protectsthe
clock, calendar, and storage registers
during power failure. A backup
battery then maintains data and oper-
ates the clock and calendar.
The bq3285E/L is a fully compatible
real-time clock for IBM AT-compatible
computers and other applications.
The only external components are a
32.768kHz crystal and a backup bat-
tery.
1
SLUS004A -DECEMBER 1993 - REVISED MAY 2004
bq3285E/L
Real-Time Clock (RTC)
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
RST Reset input
SQW Square wave output
EXTRAM Extended RAM enable
RCL RAM clear input
BC 3V backup cell input
X1–X2 Crystal inputs
V
CC Power supply
V
SS Ground
1
PN3285E1.eps
24-Pin DIP or SOIC/SSOP
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
BC
INT
RST
DS
V
SS
R/W
AS
CS
MOT
X1
X2
AD
0
AD
1
AD
2
AD
3
AD
4
AD
5
AD
6
AD
7
V
SS
RCL
Pin Connections Pin Names