The FRAM is the chonky chip to the right of the center of the board. Along the bottom we have power and interface pins.

The set of 8 tiny pads above the chip are for a different form-factor of RAM, it's normal for there not to be a chip there.

If you have the 2MBit version, you'll see RS2MT on the top of the chip. If you have the 4MBit version, you'll see RS4MT, and the chip will be a little wider.

Power Pins

  • VCC - this is the power pin. Since the chip uses 3-5VDC you should pick whatever the logic voltage you're using. For most Arduino's that's 5V.
  • 3v3 - this is the 3.3V output from the voltage regulator, you can grab up to 100mA from this if you like
  • GND - common ground for power and logic

SPI Logic pins:

All pins are 3-5V compliant and use whatever logic level is on VCC

  • SCK - This is the SPI clock pin, its an input to the chip
  • MISO - this is the Microcontroller In Serial Out pin, for data sent from the FRAM to your processor
  • MOSI - this is the Microcontroller Out Serial In pin, for data sent from your processor to the FRAM
  • CS - this is the chip select pin, drop it low to start an SPI transaction. Its an input to the chip
  • WP - Write Protect pin. This is used to write protect the status register only! This pin does not directly affect write protection for the entire chip. Instead, it protects the block-protect register which is configured however you want (sometimes only half the FRAM is protected)
  • HOLD - this is a 'wait' pin for the SPI bus. When pulled low, it puts the SPI bus on hold. This is different than the CS pin because it doesnt stop the current transaction. Its good if you want to talk to other SPI devices and stream data back and forth without stopping and starting transactions.

This guide was first published on Sep 09, 2020. It was last updated on Sep 09, 2020.

This page (Pinouts) was last updated on Oct 15, 2021.

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