FM3264/FM32256 pdf datasheet (

The FM32xx is a family of integrated devices that
includes the most commonly needed functions for
processor-based systems. Major features include
nonvolatile memory available in various sizes, low-
VDD reset, watchdog timer, nonvolatile event counter,
lockable 64-bit serial number area, and general
purpose comparator that can be used for an early
power-fail (NMI) interrupt or other purpose. The
family operates from 2.7 to 5.5V.
The FM32xx family is software and pinout
compatible with the FM31xx family which also
includes a real-time clock. The common features
allow a system design that easily can be assembled
with or without timekeeping by simply selecting the
FM31xx or FM32xx, respectively.
Each FM32xx provides nonvolatile RAM available in
sizes including 4Kb, 16Kb, 64Kb, and 256Kb
versions. Fast write speed and unlimited endurance
allow the memory to serve as extra RAM or
conventional nonvolatile storage. This memory is
truly nonvolatile rather than battery backed.