BQ3285E Datasheet, PDF (1/29 Pages) Texas Instruments – Real-Time Clock RTC

bq3285E/L
Real-Time Clock (RTC)
Features
® Direct clock/calendar replace-
ment for IBM^® AT-compatible
computers and other applications
® Functionally compatible with the
DS1285
- Closely matches MC146818A
pin configuration
® 2.7–3.6V operation (bq3285L);
4.5–5.5V operation (bq3285E)
® 242 bytes of general nonvolatile
storage
® 32.768kHz output for power man-
agement
® System wake-up capability—
alarm interrupt output active in
battery-backup mode
® Less than 0.5µA load under bat-
tery operation
® Selectable Intel or Motorola bus
timing
® 14 bytes for clock/calendar and
control
® BCD or binary format for clock
and calendar data
® Calendar in day of the week, day
of the month, months, and years,
with automatic leap-year adjust-
ment
® Time of day in seconds, minutes,
and hours
- 12- or 24-hour format
- Optional daylight saving
adjustment
® Programmable square wave out-
put
® 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
® 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.
The bq3285E/L write-protects the
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.
Pin Connections
Pin Names
MOT 1
X1 2
X2 3
AD0 4
AD1 5
AD2 6
AD3 7
AD4 8
AD5 9
AD6 10
AD7 11
VSS 12
24 VCC
23 SQW
22 EXTRAM
21 RCL
20 BC
19 INT
18 RST
17 DS
16 VSS
15 R/W
14 AS
13 CS
24-Pin DIP or SOIC/SSOP
PN3285E1.eps
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
VCC
Power supply
VSS
Ground
SLUS004A -DECEMBER 1993 - REVISED MAY 2004
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