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 (hereafter 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 programmable 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 active-low PWR output pin is triggered by one or either of these events, and is used to turn on an external power supply. The active-low PWR pin is under software control, so that when a task is complete, the system power can then be shut down.
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. 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 VCC. 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 VBAT input pin on the DS17x85 to maintain time and date operation when primary power is absent. The DS17x85 and DS17x87 include a VBAUX input used to power auxiliary functions such as active-low PWR control. The device is accessed through a multiplexed byte-wide interface.
Key Features
Applications/Uses
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)
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