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 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 system
power can then be shut down.