BQ4285_14 Datasheet, PDF (1/29 Pages) Texas Instruments – Real-Time Clock (RTC) With NVRAM Control

bq4285
Real-Time Clock ^(RTC) With NVRAM Control
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
® Automatic backup and write-
protect control to external SRAM
® 160 ns cycle time allows fast bus
operation
® Less than 0.5 µA load under bat-
tery operation
® 14 bytes for clock/calendar and
control
Pin Connections
® Calendar in day of the week, day of
the month, months, and years, with
automatic leap-year adjustment
® Time of day in seconds, minutes,
and hours
- 12- or 24-hour format
- Optional daylight saving
adjustment
® BCD or binary format for clock
and calendar data
® Programmable square wave out-
put
® Three individually maskable in-
terrupt event flags:
- Periodic rates from 122 µs to
500 ms
- 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 bq4285 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 include
three maskable interrupt sources,
square wave output, and 114 bytes of
general nonvolatile storage.
The bq4285 write-protects the clock,
calendar, and storage registers dur-
ing power failure. A backup battery
then maintains data and operates
the clock and calendar.
The bq4285 is a fully compatible real-
time clock for IBM AT-compatible com-
puters and other applications. The only
external components are a 32.768kHz
crystal and a backup battery.
The bq4285 integrates a battery-
backup controller to make a standard
CMOS SRAM nonvolatile during
power-fail conditions. During power-
fail, the bq4285 automatically write-
protects the external SRAM and pro-
vides a VCC output sourced from the
clock backup battery.
Pin Names
AD0–AD7
MOT
Multiplexed address/data
input/output
Bus type select input
VOUT 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 CEOUT
21 CEIN
20 BC
19 INT
18 RST
17 DS
16 VSS
15 R/W
14 AS
13 CS
24-Pin DIP or SOIC
PN428501.eps
SLUS002A JUNE 1991 - REVISED MAY 2004
28-Pin PLCC No longer available
CS
AS
DS
R/W
INT
RST
SQW
BC
X1–X2
NC
CEIN
CEOUT
VOUT
VCC
VSS
Chip select input
Address strobe input
Data strobe input
Read/write input
Interrupt request output
Reset input
Square wave output
3V backup cell input
Crystal inputs
No connect
RAM chip enable input
RAM chip enable output
Supply output
+5V supply
Ground
1