VIA Technologies VT82885 Manual

VIA Technologies, Inc.
FEATURES
Drop-in replacement for IBM AT computer
clock/calendar.
Pin configuration closely matches the
DS12887, DS12885and DS12885Q
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 interrpts are separately software-
maskable and testable
- Times-of-day alarm once/second to
once/day
- Periodic rates from 122 s to 500 ms
- End of clock update cycle
Optional 28-pin PLCC surface mount
package
DESCRIPTION
The VT82885 Real Time Clock is designed
to be a direct replacement for the DS12885.
The VT82885 is identical in form, fit and
function to the DS12885. It has 114 bytes of
general purpose RAM. Access to this RAM
space is 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
GND 1
X1 2
X2 3
AD0 4
AD1 5
AD2 6
AD3 7
AD4 8
AD5 9
AD6 10
AD7 11
GND 12
VT82885 24 PIN DIP
G
X X
4
N
2 1
D
5
AD0
3 2
AD1 6
AD2
7
AD3 8
AD4 9
AD5
10
NC 13 14 15 16 17
11
A N A
D C D
6 7
VT82885 28-PIN PLCC
PIN DESCRIPTION
AD0-AD7 - Multiplexed Address/Data Bus
NC - No Connection
CS# - Chip Select
AS - Address Strobe
1
VT82885
Real Time Clock
24 V
CC
23 SQW
22 NC
RCLR#
21
20 V
BAT
19 IRQ#
18 RESET#
17 RD#
16 NC
15 WR#
14 AS
13 CS#
S
V
N N
Q 26
C C
CC
W
25
RCLR#
1 28 27
24 V
BAT
23 IRQ#
22 RESET#
21 RD#
GND
20
WR#
19
G C A N
18
N S S C
D #