12885.PDF

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DS12885, DS12885Q, DS12885T
Real Time Clock
www.dalsemi.com
FEATURES
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Drop–in replacement for IBM AT computer
clock/calendar
Pin
configuration
closely
matches
MC146818B and DS1285
Counts seconds, minutes, hours, days, day of
the week, date, month, and year with leap
year compensation valid up to 2100
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
Selectable between Motorola and 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
Time–of–day alarm once/second to once/day
Periodic rates from 122
µs
to 500 ms
End of clock update cycle
Optional 28–pin PLCC surface mount
package or 32–pin TQFP
Optional industrial temperature range
available
PIN ASSIGNMENT
1 of 6
0825/99
DS12885, DS12885Q, DS12885T
DESCRIPTION
The DS12885 Real Time Clock plus RAM is designed to be a direct replacement for the DS1285. The
DS12885 is identical in form, fit, and function to the DS1285, 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. An external crystal and battery are the only components
required to maintain time–of–day and memory status in the absence of power. For a complete description
of operating conditions, electrical characteristics, bus timing, and pin descriptions other than X1, X2,
V
BAT
, and
RCLR
, see the DS12887 data sheet.
PIN DESCRIPTION
AD0–AD7
NC
MOT
CS
IRQ
AS
R/
W
DS
RESET
– Multiplexed Address/Data Bus
– No Connection
– Bus Type Selection
– Chip Select
– Address Strobe
– Read/Write Input
– Data Strobe
– Reset Input
SQW
V
CC
GND
X1,X2
V
BAT
RCLR
– Interrupt Request Output
(open drain)
– Square Wave Output
– +5 Volt Supply
– Ground
– 32.768 kHz Crystal
Connections
– +3 volt Battery Input
– RAM Clear
PIN DESCRIPTION
X1, X2 –
Connections for a standard 32.768 kHz quartz crystal. The internal oscillator circuitry is
designed for operation with a crystal having a specified load capacitance (CL) of 6 pF. The crystal is
connected directly to the X1 and X2 pins. There is no need for external capacitors or resistors. Note: X1
and X2 are very high impedance nodes. It is recommended that they and the crystal be guard–ringed with
ground and that high frequency signals be kept away from the crystal area. For more information on
crystal selection and crystal layout considerations, please consult Application Note 58, “Crystal
Considerations with Dallas Real Time Clocks.”
V
BAT
–
Battery input for any standard 3-volt lithium cell or other energy source. Battery voltage must be
held between 2.5 and 4 volts for proper operation. A maximum load of 0.5
µA
at 25°C in the absence of
power should be used to size the external energy source.
The battery should be connected directly to the V
BAT
pin. A diode must not be placed in series with the
battery to the V
BAT
pin. Furthermore, a diode is not necessary because reverse charging current protection
circuitry is provided internal to the device and has passed the requirements of Underwriters Laboratories
for UL listing.
RCLR
–
The
RCLR
pin is used to clear (set to logic 1) all 114 bytes of general purpose RAM but does
not affect the RAM associated with the real time clock. In order to clear the RAM,
RCLR
must be forced
to an input logic “0” (–0.3 to +0.8 volts) during battery back–up mode when V
CC
is not applied. The
RCLR
function is designed to be used via human interface (shorting to ground manually or by switch)
and not to be driven with external buffers. This pin is internally pulled up. Do not use an external pull–up
resistor on this pin.
2 of 6
DS12885, DS12885Q, DS12885T
DS12885 24-PIN DIP
PKG
DIM
A IN.
MM
B IN.
MM
C IN.
MM
D IN.
MM
E IN.
MM
F IN.
MM
G IN.
MM
H IN.
MM
J IN.
MM
K IN.
MM
24-PIN
MIN
MAX
1.245
1.270
31.62
32.25
0.530
0.550
13.46
13.97
0.145
0.165
3.68
4.19
0.600
0.625
15.24
15.88
0.015
0.050
0.380
1.27
0.120
0.145
3.05
3.68
0.090
0.110
2.29
2.79
0.625
0.675
15.88
17.15
0.008
0.012
0.20
0.30
0.015
0.022
0.38
0.559
3 of 6
DS12885, DS12885Q, DS12885T
DS12885 24-PIN SOIC
PKG
DIM
A IN.
MM
B IN.
MM
C IN.
MM
E IN.
MM
F IN.
MM
G IN.
MM
H IN.
MM
J IN.
MM
K IN.
MM
L IN.
MM
phi
24-PIN
MIN
MAX
0.602
0.612
15.29
15.54
0.290
0.300
7.37
7.65
0.089
0.095
2.26
2.41
0.004
0.012
0.102
0.30
0.094
0.105
2.38
2.68
0.050 BSC
1.27 BSC
0.398
0.416
10.11
10.57
0.009
0.013
0.229
0.33
0.013
0.019
0.33
0.48
0.016
0.040
0.406
1.02
0°
8°
4 of 6
DS12885, DS12885Q, DS12885T
DS12885Q 28-PIN PLCC
PKG
DIM
A IN.
MM
B IN.
MM
C IN.
MM
D IN.
MM
E IN.
MM
F IN.
MM
G IN.
MM
H IN.
MM
J IN.
MM
K IN.
MM
28-PIN
MIN
MAX
1.520
1.540
38.61
39.12
0.720
0.740
18.29
18.80
0.395
0.415
10.03
10.54
0.100
0.130
2.54
3.30
0.017
0.030
0.43
0.76
0.120
0.160
3.05
4.06
0.090
0.110
2.29
2.79
0.590
0.630
14.99
16.00
0.008
0.012
0.20
0.30
0.015
0.021
0.38
0.53
5 of 6

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