DS12B887 Datasheet, PDF (1/16 Pages) Dallas Semiconductor – Real Time Clock

DS12B887
DS12B887
Real Time Clock
FEATURES
• Drop-in replacement for IBM AT computer clock/cal-
endar
• Pin compatible with the MC146818B and DS1287
• Totally nonvolatile with over 10 years of operation in
the absence of power
• Self-contained subsystem includes lithium, quartz,
and support circuitry
• Counts seconds, minutes, hours, days, day of the
week, date, month, and year with leap year com-
pensation
• Binary or BCD representation of time, calendar, and
alarm
• 12- or 24-hour clock with AM and PM in 12-hour mode
• Daylight Savings Time option
• Multiplex bus for pin efficiency
• Interfaced with software as 128 RAM locations
– 14 bytes of clock and control registers
– 114 bytes of general purpose RAM
• Programmable square wave output signal
• Bus-compatible interrupt signals (IRQ)
• Three interrupts are separately software-maskable
and testable
– Time-of-day alarm once/second to once/day
– Periodic rates from 122 µs to 500 ms
– End of clock update cycle
PIN ASSIGNMENT
NC 1
NC 2
NC 3
AD0 4
AD1 5
AD2 6
AD3 7
AD4 8
AD5 9
AD6 10
AD7 11
GND 12
24 V_CC
23 SQW
22 NC
21 RCLR
20 NC
19 IRQ
18 NC
17 DS
16 NC
15 R/W
14 AS
13 CS
24 PIN ENCAPSULATED PACKAGE
PIN DESCRIPTION
AD0-AD7
NC
CS
AS
R/W
DS
IRQ
SQW
V_CC
GND
RCLR
– Multiplexed Address/Data Bus
– No Connection
– Chip Select
– Address Strobe
– Read/Write Input
– Data Strobe
– Interrupt Request Output
– Square Wave Output
– +5 Volt Supply
– Ground
– RAM Clear
DESCRIPTION
The DS12B887 Real Time Clock plus RAM is designed
to be a direct replacement for the DS1287A or
DS12887A. The DS12B887 is identical in form, fit, and
function to the DS1287A or DS12887A, with the excep-
tion of RCLR, and has an additional 64 bytes of general
purpose RAM. Access to this additional RAM space is
determined by the logic level presented on AD6 during
the address portion of an access cycle. A lithium energy
source, quartz crystal, and write-protection circuitry are
contained within a 24-pin dual in-line package. As such,
the DS12B887 is a complete subsystem replacing 16
components in a typical application. The functions
include a nonvolatile time-of-day clock, an alarm, a one-
hundred-year calendar, programmable interrupt,
square wave generator, and 114 bytes of nonvolatile
static RAM. The real time clock is distinctive in that
time-of-day and memory are maintained even in the
absence of power.
ECopyright 1995 by Dallas Semiconductor Corporation.
All Rights Reserved. For important information regarding
patents and other intellectual property rights, please refer to
Dallas Semiconductor data books.
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