Rev 0; 4/06
Real-Time Clocks
General Description
The DS17285, DS17485, DS17885, DS17287, DS17487,
and DS17887 real-time clocks (RTCs) are designed to be
successors to the industry-standard DS12885 and
DS12887. The DS17285, DS17485, and DS17885 (here-
after referred to as the DS17x85) provide a real-time
clock/calendar, one time-of-day alarm, three maskable
interrupts with a common interrupt output, a programma-
ble square wave, and 114 bytes of battery-backed NV
SRAM. The DS17x85 also incorporates a number of
enhanced functions including a silicon serial number,
power-on/off control circuitry, and 2k, 4k, or 8kbytes of
battery-backed NV SRAM. The DS17287, DS17487, and
DS17887 (hereafter referred to as the DS17x87) integrate
a quartz crystal and lithium energy source into a 24-pin
encapsulated DIP package. The DS17x85 and DS17x87
power-control circuitry allows the system to be powered
on by an external stimulus such as a keyboard or by a
time-and-date (wake-up) alarm. The
PWR
output pin is
triggered by one or either of these events, and is used to
turn on an external power supply. The
PWR
pin is under
software control, so that when a task is complete, the sys-
tem power can then be shut down.
For all devices, the date at the end of the month is auto-
matically adjusted for months with fewer than 31 days,
including correction for leap years. It also operates 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 DS17x85 to maintain time and date oper-
ation when primary power is absent. The DS17x85 and
DS17x87 include a V
BAUX
input used to power auxiliary
functions such as
PWR
control. The device is accessed
through a multiplexed byte-wide interface.
Features
♦
Incorporates Industry-Standard DS12887 PC
Clock Plus Enhanced Functions
♦
RTC Counts Seconds, Minutes, Hours, Day, Date,
Month, and Year with Leap Year Compensation
Through 2099
♦
Optional +3.0V or +5.0V Operation
♦
SMI Recovery Stack
♦
64-Bit Silicon Serial Number
♦
Power-Control Circuitry Supports System Power-
On from Date/Time Alarm or Key Closure
♦
Crystal Select Bit Allows Operation with 6pF or
12.5pF Crystal
♦
12-Hour or 24-Hour Clock with AM and PM in
12-Hour Mode
♦
114 Bytes of General-Purpose, Battery-Backed NV
SRAM
♦
Extended Battery-Backed NV SRAM
2048 Bytes (DS17285/DS17287)
4096 Bytes (DS17485/DS17487)
8192 Bytes (DS17885/DS17887)
♦
RAM Clear Function
♦
Interrupt Output with Six Independently Maskable
Interrupt Flags
♦
Time-of-Day Alarm Once per Second to Once per
Day
♦
End of Clock Update Cycle Flag
♦
Programmable Square-Wave Output
♦
Automatic Power-Fail Detect and Switch Circuitry
♦
Available in PDIP, SO, or TSOP Package
(DS17285, DS17485, DS17885)
♦
Optional Encapsulated DIP (EDIP) Package with
Integrated Crystal and Battery (DS17287,
DS17487, DS17887)
♦
Optional Industrial Temperature Range Available
♦
Underwriters Laboratory (UL) Recognized
Ordering Information, Pin Configurations, and Typical
Operating Circuit appear at end of data sheet.
DS17285/DS17287/DS17485/DS17487/DS17885/DS17887
Applications
Embedded Systems
Utility Meters
Security Systems
Network Hubs, Bridges, and Routers
______________________________________________
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.
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
