BQ3285_15 Datasheet, PDF (1/26 Pages) Texas Instruments – Real-Time Clock (RTC)

bq3285
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
® 114 bytes of general nonvolatile
storage
® 160ns cycle time allows fast bus
operation
® Selectable Intel or Motorola bus
timing
® Less than 0.5µA load under bat-
tery operation
® 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 or SOIC
General Description
The CMOS bq3285 is a low-power
microprocessor peripheral providing
a time-of-day clock and 100-year cal-
endar with alarm features and bat-
tery operation. Other features in-
clude three maskable interrupt
sources, square wave output, and 114
bytes of general nonvolatile storage.
The bq3285 write-protects the clock,
calendar, and storage registers during
power failure. A backup battery
then maintains data and operates the
clock and calendar.
The bq3285 is a fully compatible
real-time clock for IBM AT com-
patible computers and other appli-
cations. The only external compo-
nents are a 32.768kHz crystal and
a backup battery
Pin Connections
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 NC
21 RCL
20 BC
19 INT
18 RST
17 DS
16 VSS
15 R/W
14 AS
13 CS
24-Pin DIP or SOIC
PN328501.eps
SLUS028A - JUNE 1991 - REVISED - MAY 2004
28-Pin PLCC No longer available
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
RST
Reset input
SQW
Square wave output
RCL
RAM clear input
BC
3V backup cell input
X1–X2
Crystal inputs
NC
No connect
VCC
+5V supply
VSS
Ground