BQ4287 Datasheet, PDF (1/8 Pages) Texas Instruments – Real-Time Clock Module With NVRAM Control

bq4287
Real-Time Clock Module With NVRAM Control
Features
® Direct clock/calendar replace-
ment for IBM®
AT-compatible computers and
other applications
® Functionally compatible with the
DS1287/DS1287A and
MC146818A
® 114 bytes of general nonvolatile
storage
® Automatic backup supply and
write-protection to make external
SRAM nonvolatile
® Integral lithium cell and crystal
® 160 ns cycle time allows fast bus
operation
® Intel 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 adjustment
Pin Connections
VOUT 1
NC 2
NC 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 NC
19 INT
18 RST
17 RD
16 NC
15 WR
14 ALE
13 CS
24-Pin DIP Module
PN428701.eps
Nov. 1993 C
® 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 122 µs to
500 ms
- Time-of-day alarm once per
second to once per day
- End-of-clock update cycle
® Better than one minute per
month clock accuracy
General Description
The CMOS bq4287 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
Pin Names
AD0–AD7 Multiplexed address/data
input/output
CS
Chip select input
ALE
Address strobe input
RD
Data strobe input
WR
Read/write input
INT
Interrupt request output
RST
Reset input
SQW
Square wave output
CEIN
CEOUT
NC
RAM chip enable input
RAM chip enable output
No connect
VOUT
VCC
VSS
Supply output
+5V supply
Ground
114 bytes of general nonvolatile
storage.
The bq4287 write-protects the clock,
calendar, and storage registers dur-
ing power failure. The integral
backup energy source then main-
tains data and operates the clock
and calendar.
The bq4287 uses its integral battery-
backup controller and battery to make
a standard CMOS SRAM nonvolatile
during power-fail conditions. During
power-fail, the bq4287 automatically
write-protects the external SRAM and
provides a VCC output sourced from its
internal battery.
The bq4287 is a fully compatible
real-time clock for IBM AT-compatible
computers and other applications.
As shipped from Benchmarq, the
backup cell is electrically isolated
from the memory. Following the first
application of VCC, this isolation is
broken, and the backup cell provides
data retention to the clock, internal
RAM, VOUT, and CEOUT on subse-
quent power-downs.
The bq4287 is functionally equiva-
lent to the bq4285, except that the
battery (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 pro-
vides 130mAh of capacity. For a
complete description of features, op-
erating conditions, electrical charac-
teristics, bus timing, and pin de-
scriptions, see the bq4285 data
sheet.
Caution:
Take care to avoid inadvertent dis-
charge through V_OUT and CE_OUT
after battery isolation has been
broken.
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