The Dallas Semiconductor DS1302 Trickle Charge
Time Keeping Chip is a programmable 3–wire serial
interface clock with a trickle charge circuit for using both
rechargeable and non–rechargeable backup supplies.
The real time clock/calendar provides seconds, minutes,
hours, day, date, month, year information. The
end of the month date is automatically adjusted for
months with less than 31 days, including corrections for
leap year. The clock operates in either the 24–hour or
12–hour format with an AM/PM indicator. The DS1302
also provides 31 bytes of nonvolatile SRAM for data
storage. Interfacing the DS1302 with a microprocessor
is simplified by using a synchronous serial communication.
Only three wires are required to communicate with
the clock/RAM: (1) RST (Reset), (2) I/O (Data Line), and
(3) SCLK (Serial Clock). Data can be transferred to and
from the clock/RAM one byte at a time or in a burst of up
to 31 bytes. The DS1302 is designed to operate on very
low power and retain data and clock information on less
than 1 microwatt. The DS1302 is designed to be completely
compatible with designs that are currently using
the DS1202. This compatibility allows the DS1302 to be
dropped directly into a DS1202 socket. Then the
optional trickle charge circuit on the DS1302 can be
used to backup the system time and data with a super
cap or a rechargeable battery.