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.
The processor companion includes commonly needed
CPU support functions. Supervisory functions
include a reset output signal controlled by either a
low VDD condition or a watchdog timeout. /RST goes
active when VDD drops below a programmable
threshold and remains active for 100 ms after VDD
rises above the trip point. A programmable watchdog
timer runs from 100 ms to 3 seconds. The watchdog
timer is optional, but if enabled it will assert the reset
signal for 100 ms if not restarted by the host before
the timeout. A flag-bit indicates the source of the
reset.
A general-purpose comparator compares an external
input pin to the onboard 1.2V reference. This is
useful for generating an early warning power-fail
interrupt (NMI) but can be used for any purpose. The
family also includes a programmable 64-bit serial
number that can be locked making it unalterable.
Additionally the FM32xx offers a dual event counter
that tracks the number of rising or falling edges
detected on dedicated input pins. The counter can
optionally be battery backed and even battery
operated by attaching a backup power source to the
VBAK pin. If VBAK is connected to a battery or
capacitor, then events will be counted even in the
absence of VDD.