DS12885-DS12C887A.pdf
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19-5213; Rev 4; 4/10
Real-Time Clocks
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.
Applications
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
♦
Embedded Systems
Utility Meters
Security Systems
Network Hubs, Bridges, and Routers
Time-of-Day Alarm Once Per Second to Once
Per Day
♦
Periodic Rates from 122μs to 500ms
♦
Typical Operating Circuit
End-of-Clock Update Cycle Flag
♦
Programmable Square-Wave Output
♦
Automatic Power-Fail Detect and Switch Circuitry
♦
♦
CRYSTAL
V
CC
Optional 28-Pin PLCC Surface Mount Package or
32-Pin TQFP (DS12885)
X1
X2
V
CC
AS
RESET
Optional Encapsulated DIP (EDIP) Package with
Integrated Crystal and Battery (DS12887,
DS12887A, DS12C887, DS12C887A)
♦
Optional Industrial Temperature Range Available
♦
♦
R/W
RCLR
DS
DS83C520
DS12885
CS
AD(0–7)
SQW
Underwriters Laboratory (UL) Recognized
IRQ
V
BAT
MOT
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 Directat 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Real-Time Clocks
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
EDIP ..................................................................-40°C to +85°C
PDIP, SO, PLCC, TQFP ..................................-55°C to +125°C
Lead Temperature (soldering, 10s) .................................+260°C
(
Note:
EDIP is hand or wave-soldered only.)
Soldering Temperature (reflow)
PDIP, SO, PLCC............................................................+260°C
TQFP .............................................................................+245°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
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage
V
CC
(Note 3)
4.5
5.5
V
V
BAT
Input Voltage
V
BAT
(Note 3)
2.5
4.0
V
V
CC
+
0.3
Input Logic 1
V
IH
(Note 3)
2.2
V
Input Logic 0
V
IL
(Note 3)
-0.3
+0.8
V
V
CC
Power-Supply Current
I
CC1
(Note 4)
15
mA
V
CC
Standby Current
I
CCS
(Note 5)
mA
Input Leakage
I
IL
-1.0
+1.0
µA
I/O Leakage
I
OL
(Note 6)
-1.0
+1.0
µA
Input Current
I
MOT
(Note 7)
-1.0
+500
µA
Output at 2.4V
I
OH
(Note 3)
-1.0
mA
Output at 0.4V
I
OL
(Note 3)
4.0
mA
Power-Fail Voltage
V
PF
(Note 3)
4.0
4.25
4.5
V
VRT Trip Point
VRT
TRIP
1.3
V
2
_____________________________________________________________________
Real-Time Clocks
DC ELECTRICAL CHARACTERISTICS
(
V
CC
= 0V, V
BAT
= 3.0V
, T
A
= over the operating range, unless otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
BAT
Current (OSC On);
T
A
= +25°C, V
BACKUP
= 3.0V
I
BAT
(Note 8)
500
nA
V
BAT
Current (Oscillator Off)
I
BATDR
(Note 8)
100
nA
AC ELECTRICAL CHARACTERISTICS
(
V
CC
= 4.5V to 5.5V
, T
A
= over the operating range.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Cycle Time
t
CYC
385
DC
ns
Pulse Width, DS Low or R/W High
PW
EL
150
ns
Pulse Width, DS High or R/W Low
PW
EH
125
ns
Input Rise and Fall
t
R
, t
F
30
ns
R/W Hold Time
t
RWH
10
ns
R/W Setup Time Before DS/E
t
RWS
50
ns
Chip-Select Setup Time Before
DS or R/W
t
CS
20
ns
Chip-Select Hold Time
t
CH
0
ns
Read-Data Hold Time
t
DHR
10
80
ns
Write-Data Hold Time
t
DHW
0
ns
Address Valid Time to AS Fall
t
ASL
30
ns
Address Hold Time to AS Fall
t
AHL
10
ns
Delay Time DS/E to AS Rise
t
ASD
20
ns
Pulse Width AS High
PW
ASH
60
ns
Delay Time, AS to DS/E Rise
t
ASED
40
ns
Output Data Delay Time from DS
or R/W
t
DDR
20
120
ns
Data Setup Time
t
DSW
100
ns
Reset Pulse Width
t
RWL
5
µs
IRQ Release from DS
t
IRDS
2
µs
IRQ Release from RESET
t
IRR
2
µs
_____________________________________________________________________
3
Real-Time Clocks
Motorola Bus Read/Write Timing
PW
ASH
t
ASED
AS
t
ASD
t
CYC
PW
EL
PW
EH
DS
t
RWS
t
RWH
R/ W
t
CH
t
CS
CS
t
DSW
t
DHW
AD0–AD7
WRITE
t
ASL
t
AHL
t
DHR
AD0–AD7
READ
t
DDR
Intel Bus Write Timing
t
CYC
AS
PW
ASH
t
ASD
DS
t
ASD
t
ASED
PW
EH
R/W
PW
EL
t
CH
t
CS
CS
t
ASL
t
DSW
t
AHL
t
DHW
AD0–AD7
WRITE
4
_____________________________________________________________________
Real-Time Clocks
Intel Bus Read Timing
t
CYC
PW
ASH
AS
t
ASD
t
ASED
DS
PW
EL
PW
EH
t
ASD
R/W
t
CH
t
CS
CS
t
ASL
t
AHL
t
DDR
t
DHR
AD0–AD7
IRQRelease Delay Timing
DS
RESET
t
RWL
IRQ
t
IRR
t
IRDS
Power-Up/Power-Down Timing
V
CC
V
PF(MAX)
V
PF(MIN)
t
F
t
R
t
RPU
t
DR
DON'T CARE
RECOGNIZED
RECOGNIZED
INPUTS
HIGH-Z
VALID
OUTPUTS
VALID
_____________________________________________________________________
5
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