DS1994,pdf datasheet (4Kb Plus

The DS1994 Memory iButton is a rugged read/write data carrier that acts as a localized database, easily accessible with minimal hardware. The nonvolatile memory and optional timekeeping capability offer a simple solution to storing and retrieving vital information pertaining to the object to which the iButton is attached. Data is transferred serially through the 1-Wire protocol that requires only a single data lead and a ground return.
The scratchpad is an additional page that acts as a buffer when writing to memory. Data is first written to the scratchpad where it can be read back. After the data has been verified, a copy scratchpad command transfers the data to memory. This process ensures data integrity when modifying the memory. A 48-bit serial number is factory lasered into each DS1994 to provide a guaranteed unique identity that allows for absolute traceability. The durable MicroCan package is highly resistant to environmental hazards such as dirt, moisture, and shock. Its compact, coin-shaped profile is self-aligning with mating receptacles, allowing the DS1994 to be easily used by human operators. Accessories permit the DS1994 to be mounted on almost any surface including plastic key fobs, photo-ID badges, and PC boards.
The DS1994 also includes time-keeping functions, a real-time clock/calendar, interval timer, cycle counter, and programmable interrupts, in addition to the nonvolatile memory. The internal clock can be programmed to deny memory access based on absolute time/date, total elapsed time, or the number of accesses. These features allow the DS1994 to be used to create a stopwatch, alarm clock, time and date stamp, logbook, hour meter, calendar, system power cycle timer, interval timer, and event scheduler.