VT82887 Datasheet, PDF (1/17 Pages) List of Unclassifed Manufacturers – Real Time Clock

VIA Technologies, Inc.
VT82887
Real Time Clock
FEATURES
• Drop-in replacement for IBM AT computer
clock/calendar.
• Pin configuration closely matches the
DS12887
• 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 compensation
• 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
• Intel bus timing
• 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
- Times-of-day alarm once/second to
once/day
- Periodic rates from 122 µs to 500 ms
- End of clock update cycle
DESCRIPTION
The VT82887 Real Time Clock is designed to
be a direct replacement for the DS12887. The
VT82887 is identical in form, fit and function
to the DS12887. It has 114 bytes of general
purpose RAM. Access to this RAM space is
OPERATION
determined by the logic level presented on
AD6 during the address portion of an access
cycle. An external crystal and battery are the
only components required to maintain time-of-
day and memory status in the absence of
power. A complete description of operating
conditions, electrical characteristics, bus
timing and pin descriptions follows.
PIN ASSIGNMENT
VT82887 24 PIN DIP
GND 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 RESET#
17 RD#
16 NC
15 WR#
14 AS
13 CS#
PIN DESCRIPTION
AD0-AD7
NC
CS#
AS
WR#
RD#
RESET#
IRQ#
SQW
V_CC
GND
RCLR#
- Multiplexed Address/Data Bus
- No Connection
- Chip Select
- Address Strobe
- Write Strobe
- Read Strobe
- Reset Input
- Interrupt Request Output
- Square Wave Output
- +5 Volt Supply
- Ground
- RAM Clear
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