Identify Serial EEPROM, Flash and FRAM chips

Types of Serial memory supported #

*n = device size in Kbits, usually.

SPI Flash Memory #

SPI Flash chips use NOR memory, which is cheap, fast, and small. There are several trade offs though:

• Size: 1 Mbit to 512 Mbit (128K - 64M)
• Read: Not byte addressable, data must be read in whole pages (usually 256 bytes) at a time.
• Write: Not byte addressable, data must be written in whole pages (usually 256 bytes) at a time and page aligned.
• Erase: Data must be erased in whole sectors (usually 4K, 8K or 64K) at a time.
• Cost: SPI Flash is cheap!
• Write cycles: 10,000+
• Data retention: 20 years

To update existing data, you must first read all the data in the erase sector, modify it in RAM, erase the whole 4K sector, and then write it back to the flash memory.

Identifying SPI Flash chips #

A really common SPI Flash chip is the Winbond W25Qnnn series. It will be labeled with the Winbond logo and the part number will start with “W25Q” followed by a three digit number indicating the size in Mbits.

Most recent SPI flash chips have their characteristics stored in JEDEC standard SFDP (Serial Flash Discoverable Parameters) format. The flash command in SPI mode will automatically read the SFDP data and display the chip characteristics, including the manufacturer, size, erase sector size, and other parameters.

If SFDP data isn’t available, the flash command has a database of known chips and can identify them by their JEDEC ID.

EEPROM memory #

Unlike Flash (NOR) memory, EEPROM memory is byte-addressable and can be written to one byte at a time.

• Size: 1Kbit to 4 Mbit (128B - 512K)
• Read: Byte addressable, can read any byte in the chip.
• Write: 1 byte up to the page size (8 to 256 bytes, depending on chip) at a time. Writes must be aligned to the page size.
• Erase: No separate erase process is needed, bytes are erased individually before writing.
• Cost: EEPROM is generally more expensive than NOR Flash memory.
• Write cycles: 1,000,000+
• Data retention: 100-200 years

Identifying SPI EEPROM chips #

SPI EEPROM chips are usually labeled with a part number starting with “25” or “95”. The “25” series is more common and includes chips like AT25C020, 25LC040, 25AA080, etc. The “95” series is STM’s name for their 25x compatible EEPROMs, just substitute the same sized 25x part, e.g. 25LC040 is equivalent to 95LC040.

SPI EEPROM voltage requirements #

Identifying I2C EEPROM chips #

I2C EEPROM chips are usually labeled with a part number starting with “24”. The “24” series includes chips like 24LC02, 24AA04, AT2402 etc. The “24” series is the most common I2C EEPROM series.

I2C EEPROM voltage requirements #

Identifying 1-Wire EEPROM chips #

1-Wire EEPROMs are slightly different than SPI and I2C EEPROMs. Writes must be a full page (8 or 32 bytes) at a time, and they have much lower write cycles and data retention than SPI or I2C EEPROMs.

• Write: A full page (8 or 32 bytes), write aligned to the page size.
• Write cycles: 200,000
• Data retention: 10-25 years

1-Wire EEPROM chips are usually labeled with a part number starting with “243”. The “243” series includes chips like DS2431, DS2432, GX2341, DS24B33, etc. The “243” series is the only known series of 1-Wire EEPROMs.

1-Wire EEPROM voltage requirements #

Identifying Microwire EEPROM chips #

Microwire EEPROM chips are ancient technology that persists today. Microwire EEPROMs are also byte-addressable and can be written to one byte at a time. They use a funky version of SPI and have a drastically different pinout.

Microwire EEPROM chips are usually labeled with a part number starting with “93”. The “93” series includes chips like 93C46A, 93C56B, 93C66C, etc.

For 93xxxC chips, the ORG pin determines the addressing mode:

• LOW/GROUND: 8-bit addressing
• HIGH/VCC: 16-bit addressing

Find and measure the ORG pin with a multimeter to determine the addressing mode. The most common pinout is the example on the right (PDIP/SIOC), though a rarer “rotated pinout” version seems to exist.

Image source: Microchip 93xx46 datasheet

Microwire EEPROM voltage requirements #

FRAM Memory #

SPI FRAM chips are a type of non-volatile memory that uses ferroelectric RAM technology. They are faster than EEPROM and Flash. FRAM can be written one byte at a time, or continuously without stop. FRAM has a very high write endurance and can be used in applications that require frequent writes.

• Size: 1Kbit to 4 Mbit (128B - 512K)
• Read: Byte addressable, can read any byte in the chip.
• Write: Continuous write, can write any byte in the chip. No concept of pages or sectors.
• Erase: No separate erase process is needed, bytes are erased individually before writing.
• Cost: FRAM is the most expensive memory in wide spread use, but is becoming more affordable.
• Write cycles: 10^15+ (1,000,000 times more than EEPROM)
• Data retention: 100+ years

Identifying SPI FRAM chips #

SPI FRAM chips are usually labeled with a part number starting with “FM25” or “MB85”. The “FM25” series includes chips like FM25CL64B, FM25L04B, etc. The MB85RS series is Infineon’s name for their FRAM chips, e.g. MB85RS512.

Identifying I2C FRAM chips #

I2C FRAM chips are usually labeled with a part number starting with “FM24” or “MB85”. The “FM24” series includes chips like FM24CL64B, FM24L04B, etc. The MB85RC series is Infineon’s name for their FRAM chips, e.g. MB85RC64.

FRAM voltage requirements #