bq3287/bq3287A
Real-Time Clock (RTC) Module
Features
® Direct clock/calendar replacement for IBM ® AT-compatible
computers and other applications
® Functionally compatible with the
DS1287/DS1287A and MC146818A
® 114 bytes of general nonvolatile
storage
® Calendar in day of the week, day
of the month, months, and years
with automatic leap-year adjustment
® Programmable square wave output
® Three individually maskable interrupt event flags:
-
® Selectable Intel or Motorola bus
timing
Time-of-day alarm once per
second to once per day
-
® 160 ns cycle time allows fast bus
operation
Periodic rates from 122 µs to
500 ms
-
® Integral lithium cell and crystal
End-of-clock update cycle
® 14 bytes for clock/calendar and
control
® Better than one minute per
month clock accuracy
® BCD or binary format for clock
and calendar data
General Description
® Time of day in seconds, minutes,
and hours
-
12- or 24-hour format
-
Optional daylight saving
adjustment
Pin Connections
The CMOS bq3287/bq3287A is a
low-power microprocessor peripheral providing a time-of-day clock
and 100-year calendar with alarm
features and battery operation.
O t he r f e a tu re s i n cl u d e th re e
maskable interrupt sources, squarewave output, and 114 bytes of gene r al n o n volatile storage. The
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
The bq3287 is a fully compatible
r e a l - t i m e c l o c k f o r I B M ATcompatible computers and other app l i c a t i o n s. T h e b q 3 2 8 7 w r i t e protects the clock, calendar, and
storage registers during power failure. The integral backup energy
source then maintains data and operates the clock and calendar.
As shipped from Benchmarq, the
real time clock is turned off to maximize battery capacity for in-system
operation.
The bq3287 is functionally equivalent to the bq3285, except that the
battery (16, 20) and crystal (2, 3)
pins are not accessible. These pins
are connected internally to a coin
cell and quartz crystal. The coin cell
is sized to provide 10 years of data
retention and clock operation in the
absence of power. For a complete description of features, operating conditions, electrical characteristics,
bus timing, and pin descriptions, see
the bq3285 data sheet.
Pin Names
AD0–AD7
MOT
NC
NC
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
VSS
bq3287A version is identical to the
bq3287, with the addition of the RAM
clear input.
VCC
SQW
NC
NC/RCL
NC
INT
RST
DS
NC
R/W
AS
CS
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
24-Pin DIP Module
PN328701.eps
Sept. 1996 D
1
RST
Reset input
SQW
Square wave output
NC
No connect
RCL
RAM clear input
(bq3287A only)
VCC
+5V supply
VSS
Ground
