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FM3164/FM31256: 64-Kbit/256-Kbit Integrated Processor Companion with F-RAM | Cypress Semiconductor

FM3164/FM31256: 64-Kbit/256-Kbit Integrated Processor Companion with F-RAM

Last Updated: 
May 28, 2020


  • 64-Kbit/256-Kbit ferroelectric random access memory (F-RAM)
    • Logically organized as 8 K × 8 (FM3164) / 32 K × 8 (FM31256)
    • High-endurance 100 trillion (1014) read/writes
    • 151-year data retention (See the Data Retention and Endurance table)
    • NoDelay™ writes
    • Advanced high-reliability ferroelectric process
  • High Integration Device Replaces Multiple Parts
    • Serial nonvolatile memory
    • Real time clock (RTC)
    • Low voltage reset
    • Watchdog timer
    • Early power-fail warning/NMI
    • Two 16-bit event counter
    • Serial number with write-lock for security
  • Real-time Clock/Calendar
    • Backup current at 2 V: 1.15 μA at +25 °C
    • Seconds through centuries in BCD format
    • Tracks leap years through 2099
    • Uses standard 32.768 kHz crystal (6 pF)
    • Software calibration
    • Supports battery or capacitor backup
  • Processor Companion
    • Active-low reset output for VDD and watchdog
    • Programmable low-VDD reset trip point
    • Manual reset filtered and debounced
    • Programmable watchdog timer
    • Dual Battery-backed event counter tracks system intrusions or other events
    • Comparator for power-fail interrupt
    • 64-bit programmable serial number with lock
  • Fast 2-wire serial interface (I2C)
    • Up to 1-MHz frequency
    • Supports legacy timings for 100 kHz and 400 kHz
    • RTC, Supervisor controlled via I2C interface
    • Device select pins for up to 4 memory devices
  • Low power consumption
    • 1.5 mA active current at 1 MHz
    • 150 μA standby current
  • Operating voltage: VDD = 2.7 V to 5.5 V
  • Industrial temperature: –40 °C to +85 °C
  • 14-pin small outline integrated circuit (SOIC) package
  • Restriction of hazardous substances (RoHS) compliant

Functional Overview

The FM3164/FM31256 device integrates F-RAM memory with the most commonly needed functions for processor-based systems. Major features include nonvolatile memory, real time clock, low-VDD reset, watchdog timer, nonvolatile event counter, lockable 64-bit serial number area, and general purpose comparator that can be used for a power-fail (NMI) interrupt or any other purpose.

The FM3164/FM31256 is a 64-Kbit/256-Kbit nonvolatile memory employing an advanced ferroelectric process. A ferroelectric random access memory or F-RAM is nonvolatile and performs reads and writes similar to a RAM. This memory is truly nonvolatile rather than battery backed. It provides reliable data retention for 151 years while eliminating the complexities, overhead, and system-level reliability problems caused by other nonvolatile memories. The FM3164/FM31256 is capable of supporting 1014 read/write cycles, or 100 million times more write cycles than EEPROM.

The real time clock (RTC) provides time and date information in BCD format. It can be permanently powered from an external backup voltage source, either a battery or a capacitor. The timekeeper uses a common external 32.768 kHz crystal and provides a calibration mode that allows software adjustment of timekeeping accuracy.

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 comparator on PFI compares an external input pin to the onboard 1.2 V reference. This is useful for generating a 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 it offers a dual battery-backed event counter that tracks the number of rising or falling edges detected on a dedicated input pin.

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