Arduino library for I2C FRAM.

FRAM is a library to read from and write to (over I2C) an FRAM module. The library has (since 0.4.0) two classes FRAM and FRAM32. The first is for the 16 bit devices and the latter for the 32 bit devices. Currently only the MB85RC1MT is known to be 32 bit. FRAM32 can also address 16 bit devices although there is some overhead in footprint.

FRAM stands for Ferroelectric RAM - https://en.wikipedia.org/wiki/Ferroelectric_RAM

FRAM memory is much faster than EEPROM and almost as fast as (Arduino UNO) RAM. Another important feature FRAM has in common with EEPROM is that FRAM keeps its content after a reboot as it is non-volatile, even for years. That makes it ideal to store configuration or logging data in a project.

Types of FRAM that should work with this library:

• Not all types of FRAM are tested. Please let me know if you have verified one that is not in the list.
• If there is no deviceID getSize() will not work correctly.
• Address = 0x50 (default) .. 0x57, depends on the lines A0..A2.
• MB85RC1MT uses even addresses only as it uses the next odd one internally. So 0x50 uses 0x51 internally for the upper 64 KB block. This latter will not be shown on an I2C scanner (to be tested).

• FRAM(TwoWire *wire = &Wire) Constructor with optional Wire interface.
• FRAM32(TwoWire *wire = &Wire) Constructor with optional Wire interface, specific for MB85RC1MT type of device.
• int begin(uint8_t address = 0x50, int8_t writeProtectPin = -1) address and writeProtectPin is optional. Note the MB85RC1MT only uses even addresses.
• int begin(int sda, int scl, uint8_t address = 0x50, int8_t writeProtectPin = -1) idem for ESP32 a.o.
• bool isConnected() checks if the address is visible on the I2C bus.

Support for basic types and 2 calls for generic object, use casting if needed. In the FRAM32 class these functions have an uin32_t memaddr.

• void write8(uint16_t memaddr, uint8_t value) uint8_t
• void write16(uint16_t memaddr, uint16_t value) uint16_t
• void write32(uint16_t memaddr, uint32_t value) uint32_t
• void writeFloat(uint16_t memaddr, float value) float (since 0.4.3)
• void writeDouble(uint16_t memaddr, double value) double (since 0.4.3) For board that have 8 byte double.
• void write(uint16_t memaddr, uint8_t * obj, uint16_t size) other types / sizes.
• uint8_t read8(uint16_t memaddr)
• uint16_t read16(uint16_t memaddr)
• uint32_t read32(uint16_t memaddr)
• float readFloat(uint16_t memaddr) (since 0.4.3)
• double readDouble(uint16_t memaddr) (since 0.4.3) For board that have 8 byte double.
• void read(uint16_t memaddr, uint8_t uint8_t * obj, uint16_t size) One needs to allocate memory as the function won't.

(0.3.4 added template functions, see issue #13 )

• uint16_t writeObject(uint16_t memaddr, T &obj) writes an object to memaddr (and following bytes). Returns memaddr + sizeof(obj) to get the next address to write to.
• uint16_t readObject(uint16_t memaddr, T &obj) reads an object from memaddr and next bytes. Returns memaddr + sizeof(obj) to get the next address to read from.

(0.3.5 added)

• uint32_t clear(uint8_t value = 0) clears the whole FRAM by writing value to all addresses - default zero's. Returns the number of bytes written.

• bool setWriteProtect(bool b) make the FRAM write-protected by pulling line HIGH / LOW. Returns true if a writeProtectPin was defined. Otherwise the FRAM cannot be write protected. Note the pin should be defined in begin().
• bool getWriteProtect() get current write protect status.
• uint16_t getManufacturerID() idem. Fujitsu = 0x00A.
• uint16_t getProductID() idem. Proprietary.
• uint16_t getSize() returns size in kiloBYTE. If the FRAM has no device ID, the size cannot be read.
• uint32_t getSizeBytes() returns size in BYTES. Convenience wrapper, useful for iterating over the whole memory, or testing the upper boundary.
• void setSizeBytes(uint32_t value) sets size in bytes for getSizeBytes(). To be used only if getSize() cannot determine the size. See also remark in Future section below.

(0.3.6 added - experimental)

• void sleep() puts the FRAM in sleep mode so it uses less power. Still needs a power test for several types of FRAM.
• bool wakeup(uint32_t trec = 400) tries to wake up the device with a default recovery time of 400 microseconds. Returns true if connected after the call.

According to the data sheets there are only three FRAM devices support the sleep command. So use with care.

current with * are from datasheet

Indicative power usage in uA in three modi (if supported).

TODO: fill the table

See examples

Since version 0.4.2 a separate class FRAM_RINGBUFFER is added.= to this repo. Its interface is pretty straightforward and described in FRAM_RINGBUFFER.md. The FRAM_ringbuffer.ino examples shows how the class can be used.

• improve FRAM32 that can write over the 64 KB border without problems.
  • Would cause extra checking ==> overhead.
  • now it is responsibility user.
  • do we want/need this?

• write() and writeBlock() might write beyond the end of FRAM
  • now it is responsibility user.
  • testing would degrade performance?
  • error flag ?
• extend examples
  • FRAM for multi language string storage
  • FRAM logging, unequal length strings.
  • FRAM (8x) concatenated as one continuous memory.

• test more types of FRAM
• getSize() scanning FRAM like EEPROM library?
• remember last written address? why?
• fill power usage table (documentation)

• extend current clear() with partial clear(begin, end, value)?
  • can be done by writeBlock() calls by user too
  • would need more complex end checking
  • ==> wont for now
• dump(stream) or printable interface?
  • Print interface? expensive in performance per char..