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FM33256B: 256-Kbit (32 K × 8) Integrated Processor Companion with F-RAM | Cypress Semiconductor

FM33256B: 256-Kbit (32 K × 8) Integrated Processor Companion with F-RAM

Last Updated: 
Jun 26, 2020


  • 256-Kbit ferroelectric random access memory (F-RAM)
    • Logically organized as 32 K × 8
    • 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) with alarm
    • Low VDD detection drives reset
    • Watchdog window timer
    • Early power-fail warning / NMI
    • 16-bit nonvolatile 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/12.5 pF)
    • Software calibration
    • Supports battery or capacitor backup
  • Processor Companion
    • Active-low reset output for VDD and watchdog
    • Programmable low-VDD reset thresholds
    • Manual reset filtered and debounced
    • Programmable watchdog window timer
    • Nonvolatile event counter tracks system intrusions or other events
    • Comparator for power-fail interrupt or other use
    • 64-bit programmable serial number with lock
  • Fast serial peripheral interface (SPI)
    • Up to 16-MHz frequency
    • RTC, Supervisor controlled via SPI interface
    • Supports SPI mode 0 (0, 0) and mode 3 (1, 1)
  • Low power consumption
    • 1.1 mA active current at 1 MHz
    • 150 μA standby current
  • Operating voltage: VDD = 2.7 V to 3.6 V
  • Industrial temperature: –40 °C to +85 °C
  • 14-pin small outline integrated circuit (SOIC) package
  • Restriction of hazardous substances (RoHS) compliant
  • Underwriters laboratory (UL) recognized

Functional Overview

The FM33256B 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 FM33256B is a 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. It provides reliable data retention for 151 years while eliminating the complexities, overhead, and system-level reliability problems caused by other nonvolatile memories. The FM33256B 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 (max.) after VDD rises above the trip point. A programmable watchdog timer runs from 60 ms to 1.8 seconds. The timer may also be programmed for a delayed start, which functions as a window timer. The watchdog timer is optional, but if enabled it will assert the reset signal for 100 ms if not restarted by the host within the time window. A flag-bit indicates the source of the reset.

A comparator on PFI compares an external input pin to the onboard 1.5 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 an event counter that tracks the number of rising or falling edges detected on a dedicated input pin. The counter can be programmed to be nonvolatile under VDD power or battery-backed using only VBAK. If VBAK is connected to a battery or capacitor, then events will be counted even in the absence of VDD.

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