1
VT82885
Real Time Clock
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
µ
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
1
2
GND
3
4
5
X1
X2
AD0
AD1
24
V
CC
23
22
21
20
19
18
17
SQW
NC
RCLR#
V
BAT
IRQ#
RESET#
RD#
6
7
8
AD2
AD3
AD4
AD5
AD6
AD7
GND
9
10
11
12
16
15
14
13
NC
WR#
AS
CS#
VT82885 24 PIN DIP
AD0
AD1
AD2
AD3
AD4
AD5
NC
RCLR#
V
BAT
IRQ#
RESET#
RD#
GND
WR#
X
2
X
1
G
N
D
N
C
V
CC
S
Q
W
N
C
A
D
6
N
C
A
D
7
G
N
D
C
S
#
A
S
N
C
1
2
7
6
3
9
8
10
13 14 15 16 17
20
21
22
23
24
27
28
25
11
19
18
4
26
5
VT82885 28-PIN PLCC
PIN DESCRIPTION
AD0-AD7
- Multiplexed Address/Data Bus
NC
- No Connection
CS#
- Chip Select
AS
- Address Strobe
