Rev 3; 2/07
Real-Time Clock
General Description
The DS12885, DS12887, and DS12C887 real-time
clocks (RTCs) are designed to be direct replacements
for the DS1285 and DS1287. The devices provide a
real-time clock/calendar, one time-of-day alarm, three
maskable interrupts with a common interrupt output, a
programmable square wave, and 114 bytes of battery-
backed static RAM (113 bytes in the DS12C887 and
DS12C887A). The DS12887 integrates a quartz crystal
and lithium energy source into a 24-pin encapsulated
DIP package. The DS12C887 adds a century byte at
address 32h. For all devices, the date at the end of the
month is automatically adjusted for months with fewer
than 31 days, including correction for leap years. The
devices also operate in either 24-hour or
12-hour format with an AM/PM indicator. A precision
temperature-compensated circuit monitors the status of
V
CC
. If a primary power failure is detected, the device
automatically switches to a backup supply. A lithium
coin-cell battery can be connected to the V
BAT
input
pin on the DS12885 to maintain time and date operation
when primary power is absent. The device is accessed
through a multiplexed byte-wide interface, which sup-
ports both Intel and Motorola modes.
Features
♦
Drop-In Replacement for IBM AT Computer
Clock/Calendar
♦
RTC Counts Seconds, Minutes, Hours, Day, Date,
Month, and Year with Leap Year Compensation
Through 2099
♦
Binary or BCD Time Representation
♦
12-Hour or 24-Hour Clock with AM and PM in
12-Hour Mode
♦
Daylight Saving Time Option
♦
Selectable Intel or Motorola Bus Timing
♦
Interfaced with Software as 128 RAM Locations
♦
14 Bytes of Clock and Control Registers
♦
114 Bytes of General-Purpose, Battery-Backed
RAM (113 Bytes in the DS12C887 and
DS12C887A)
♦
RAM Clear Function (DS12885, DS12887A, and
DS12C887A)
♦
Interrupt Output with Three Independently
Maskable Interrupt Flags
♦
Time-of-Day Alarm Once Per Second to Once
Per Day
♦
Periodic Rates from 122μs to 500ms
♦
End-of-Clock Update Cycle Flag
♦
Programmable Square-Wave Output
♦
Automatic Power-Fail Detect and Switch Circuitry
♦
Optional 28-Pin PLCC Surface Mount Package or
32-Pin TQFP (DS12885)
♦
Optional Encapsulated DIP (EDIP) Package with
Integrated Crystal and Battery (DS12887,
DS12887A, DS12C887, DS12C887A)
♦
Optional Industrial Temperature Range Available
♦
Underwriters Laboratory (UL) Recognized
DS12885/DS12887/DS12887A/DS12C887/DS12C887A
Applications
Embedded Systems
Utility Meters
Security Systems
Network Hubs, Bridges, and Routers
Typical Operating Circuit
CRYSTAL
V
CC
X1
AS
R/W
DS
X2
V
CC
RESET
RCLR
DS83C520
CS
AD(0–7)
IRQ
MOT
DS12885
SQW
V
BAT
GND
Pin Configurations and Ordering Information appear at end of data sheet.
______________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Real-Time Clock
DS12885/DS12887/DS12887A/DS12C887/DS12C887A
ABSOLUTE MAXIMUM RATINGS
Voltage Range on V
CC
Pin Relative to Ground .....-0.3V to +6.0V
Operating Temperature Range ...................................................
Commercial (noncondensing) .............................0°C to +70°C
Operating Temperature Range ...................................................
Industrial (noncondensing)...............................-40°C to +85°C
Storage Temperature Range .............................-55°C to +125°C
Soldering Temperature .......................................See IPC/JEDEC
J-STD-020 Specification (Note 1)
Soldering Temperature (leads, 10s) ................................+260°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(V
CC
= +4.5V to +5.5V,
T
A
= over the operating range, unless otherwise noted.) (Note 2)
PARAMETER
Supply Voltage
V
BAT
Input Voltage
Input Logic 1
Input Logic 0
V
CC
Power-Supply Current
V
CC
Standby Current
Input Leakage
I/O Leakage
Input Current
Output at 2.4V
Output at 0.4V
Power-Fail Voltage
VRT Trip Point
SYMBOL
V
CC
V
BAT
V
IH
V
IL
I
CC1
I
CCS
I
IL
I
OL
I
MOT
I
OH
I
OL
V
PF
VRT
TRIP
(Note 6)
(Note 7)
(Note 3)
(Note 3)
(Note 3)
4.0
4.25
1.3
(Note 3)
(Note 3)
(Note 3)
(Note 3)
(Note 4)
(Note 5)
-1.0
-1.0
-1.0
-1.0
4.0
4.5
+1.0
+1.0
+500
CONDITIONS
MIN
4.5
2.5
2.2
-0.3
TYP
MAX
5.5
4.0
V
CC
+
0.3
+0.8
15
UNITS
V
V
V
V
mA
mA
µA
µA
µA
mA
mA
V
V
2
_____________________________________________________________________
Real-Time Clock
DC ELECTRICAL CHARACTERISTICS
(V
CC
= 0V, V
BAT
= 3.0V,
T
A
= over the operating range, unless otherwise noted.) (Note 2)
PARAMETER
V
BAT
Current (OSC On);
T
A
= +25°C, V
BACKUP
= 3.0V
V
BAT
Current (Oscillator Off)
SYMBOL
I
BAT
I
BATDR
(Note 8)
(Note 8)
CONDITIONS
MIN
TYP
MAX
500
100
UNITS
nA
nA
DS12885/DS12887/DS12887A/DS12C887/DS12C887A
AC ELECTRICAL CHARACTERISTICS
(V
CC
= 4.5V to 5.5V,
T
A
= over the operating range.) (Note 2)
PARAMETER
Cycle Time
Pulse Width, DS Low or R/W High
Pulse Width, DS High or R/W Low
Input Rise and Fall
R/W Hold Time
R/W Setup Time Before DS/E
Chip-Select Setup Time Before
DS or R/W
Chip-Select Hold Time
Read-Data Hold Time
Write-Data Hold Time
Address Valid Time to AS Fall
Address Hold Time to AS Fall
Delay Time DS/E to AS Rise
Pulse Width AS High
Delay Time, AS to DS/E Rise
Output Data Delay Time from DS
or R/W
Data Setup Time
Reset Pulse Width
IRQ
Release from DS
IRQ
Release from
RESET
SYMBOL
t
CYC
PW
EL
PW
EH
t
R
, t
F
t
RWH
t
RWS
t
CS
t
CH
t
DHR
t
DHW
t
ASL
t
AHL
t
ASD
PW
ASH
t
ASED
t
DDR
t
DSW
t
RWL
t
IRDS
t
IRR
10
50
20
0
10
0
30
10
20
60
40
20
100
5
2
2
120
80
CONDITIONS
MIN
385
150
125
30
TYP
MAX
DC
UNITS
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
µs
µs
µs
_____________________________________________________________________
3
NXP MCU
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