Arduino library to support external I2C EEPROMs.
C++

ReadMe.md

Arduino External EEPROM Library v3

http://github.com/JChristensen/extEEPROM ReadMe file
Jack Christensen Jul 2014

CC BY-SA

Introduction

Arduino External EEPROM Library

This library will work with most I2C serial EEPROM chips between 2k bits and 2048k bits (2M bits) in size. Multiple EEPROMs on the bus are supported as a single address space. I/O across block, page and device boundaries is supported. Certain assumptions are made regarding the EEPROM device addressing. These assumptions should be true for most EEPROMs but there are exceptions, so read the datasheet and know your hardware.

The library should also work for EEPROMs smaller than 2k bits, assuming that there is only one EEPROM on the bus and also that the user is careful to not exceed the maximum address for the EEPROM.

The extEEPROM Library has been tested with:

  • Microchip 24AA02E48 (2k bit)
  • 24xx32 (32k bit, thanks to Richard M)
  • Microchip 24LC256 (256k bit)
  • Microchip 24FC1026 (1M bit, thanks to Gabriele B on the Arduino forum)
  • ST Micro M24M02 (2M bit)

The extEEPROM Library will NOT work with Microchip 24xx1025 as its control byte does not conform to the following assumptions.

Device addressing assumptions:

  • The I2C address sequence consists of a control byte followed by one address byte (for EEPROMs <= 16k bits) or two address bytes (for EEPROMs > 16k bits).
  • The three least-significant bits in the control byte (excluding the R/W bit) comprise the three most-significant bits for the entire address space, i.e. all chips on the bus. As such, these may be chip-select bits or block-select bits (for individual chips that have an internal block organization), or a combination of both (in which case the block-select bits must be of lesser significance than the chip-select bits).
  • Regardless of the number of bits needed to address the entire address space, the three most-significant bits always go in the control byte. Depending on EEPROM device size, this may result in one or more of the most significant bits in the I2C address bytes being unused (or "don't care" bits).
  • An EEPROM contains an integral number of pages.

Note that the Arduino Wire library has a buffer size of 32 bytes. This limits the size of physical I/Os that can be done to EEPROM. For writes, one or two bytes are used for the address, so writing is therefore limited to 31 or 30 bytes. Because the extEEPROM Library will handle I/O across block, page and device boundaries, the only consequence this has for the user is one of efficiency; arbitrarily large blocks of data can be written and read; however, carefully chosen block sizes may reduce the number of physical I/Os needed.

"Arduino External EEPROM Library" by Jack Christensen is licensed under CC BY-SA 4.0.

Installation

To use the extEEPROM Library:

  • Go to http://github.com/JChristensen/extEEPROM, click the Download ZIP button and save the ZIP file to a convenient location on your PC.
  • Uncompress the downloaded file. This will result in a folder containing all the files for the library, that has a name that includes the branch name, usually extEEPROM-master.
  • Rename the folder to just extEEPROM.
  • Copy the renamed folder to the Arduino sketchbook\libraries folder.

Examples

The following example sketch is included with the extEEPROM Library:

  • eepromTest: Writes 32-bit integers to the entire EEPROM address space, starting at address 0 and continuing to the topmost address. These are then read back in and verified; any discrepancies are reported to the serial monitor.

Usage notes

The extEEPROM Library is designed for use with Arduino version 1.0 or later.

To use the extEEPROM Library, the standard Arduino Wire library must also be included. For brevity, this include is not repeated in the examples below:

#include <Wire.h>         //http://arduino.cc/en/Reference/Wire (included with Arduino IDE)

Enumerations

eeprom_size_t

Description

EEPROM device size in k-bits. Many manufacturers' EEPROM part numbers are designated in k-bits.

Values
  • kbits_2
  • kbits_4
  • kbits_8
  • kbits_16
  • kbits_32
  • kbits_64
  • kbits_128
  • kbits_256
  • kbits_512
  • kbits_1024
  • kbits_2048

twiClockFreq_t

Description

I2C bus speed.

Values
  • extEEPROM::twiClock100kHz
  • extEEPROM::twiClock400kHz

Constructor

extEEPROM(eeprom_size_t devCap, byte nDev, unsigned int pgSize, byte busAddr)

Description

Instantiates an external EEPROM object.

Syntax

extEEPROM myEEPROM(eeprom_size_t devCap, byte nDev, unsigned int pgSize, byte busAddr));

Parameters

devCap (eeprom_size_t): The size of one EEPROM device in k-bits. Choose a value from the eeprom_size_t enumeration above.
nDev (byte): The number of EEPROM devices on the bus. Note that if there are multiple EEPROM devices on the bus, they must be identical and each must have its address pins strapped properly.
pgSize (unsigned int): The EEPROM page size in bytes. Consult the datasheet if you are unsure of the page size.
busAddr (byte): The base I2C bus address for the EEPROM(s). 0x50 is a common value and this parameter can be omitted, in which case 0x50 will be used as the default.

Example
extEEPROM myEEPROM(kbits_256, 2, 64);           //two 24LC256 EEPROMS on the bus
extEEPROM oddEEPROM(kbits_8, 1, 16, 0x42);      //an EEPROM with a non-standard I2C address

Methods

begin(twiClockFreq_t freq)

Description

Initializes the library. Call this method once in the setup code. begin() does a dummy I/O so that the user may interrogate the return status to ensure the EEPROM is operational.

Syntax

myEEPROM.begin(twiClockFreq_t freq);

Parameters

freq (twiClockFreq_t): The desired I2C bus speed, extEEPROM::twiClock100kHz or extEEPROM::twiClock400kHz. Can be omitted in which case it will default to twiClock100kHz. NOTE: When using 400kHz, if there are other devices on the bus they must all support a 400kHz bus speed. Secondly, the other devices should be initialized first, as other libraries may not support adjusting the bus speed. To ensure the desired speed is set, call the extEEPROM.begin() function after initializing all other I2C devices.

Returns

I2C I/O status, zero if successful (byte). See the Arduino Wire.endTransmission() function for a description of other return codes.

Example
extEEPROM myEEPROM(kbits_256, 2, 64);
byte i2cStat = myEEPROM.begin(extEEPROM::twiClock400kHz);
if ( i2cStat != 0 ) {
    //there was a problem
}

write(unsigned long addr, byte *values, unsigned int nBytes)

Description

Write one or more bytes to external EEPROM.

Syntax

myEEPROM.write(unsigned long addr, byte* values, byte nBytes);

Parameters

addr (unsigned long): The beginning EEPROM location to write.
values (byte*): Pointer to an array containing the data to write.
nBytes (unsigned int): The number of bytes to write.

Returns

I2C I/O status, zero if successful (byte). See the Arduino Wire.endTransmission() function for a description of other return codes. Returns a status of EEPROM_ADDR_ERR if the I/O would extend past the top of the EEPROM address space.

Example
byte myData[10];
//write 10 bytes starting at location 42
byte i2cStat = myEEPROM.write(42, &data, 10);
if ( i2cStat != 0 ) {
    //there was a problem
    if ( i2cStat == EEPROM_ADDR_ERR) {
        //bad address
    }
    else {
        //some other I2C error
    }
}

write(unsigned long addr, byte value)

Description

Writes a single byte to external EEPROM.

Syntax

myEEPROM.write(unsigned long addr, byte value);

Parameters

addr (unsigned long): The EEPROM location to write.
values (byte): The value to write.

Returns

Same as multiple-byte write() above.

Example
//write the value 16 to EEPROM location 314.
byte i2cStat = myEEPROM.write(314, 16);

read(unsigned long addr, byte *values, unsigned int nBytes)

Description

Reads one or more bytes from external EEPROM into an array supplied by the caller.

Syntax

myEEPROM.read(unsigned long addr, byte *values, byte nBytes);

Parameters

addr (unsigned long): The beginning EEPROM location to read from.
values (byte*): Pointer to an array to receive the data.
nBytes (unsigned int): The number of bytes to read.

Returns

I2C I/O status, zero if successful (byte). See the Arduino Wire.endTransmission() function for a description of other return codes. Returns a status of EEPROM_ADDR_ERR if the I/O would extend past the top of the EEPROM address space.

Example
byte myData[10];
//read 10 bytes starting at location 42
byte i2cStat = myEEPROM.read(42, &data, 10);
if ( i2cStat != 0 ) {
    //there was a problem
    if ( i2cStat == EEPROM_ADDR_ERR) {
        //bad address
    }
    else {
        //some other I2C error
    }
}

read(unsigned long addr)

Description

Reads a single byte from external EEPROM.

Syntax

myEEPROM.read(unsigned long addr);

Parameters

addr (unsigned long): The EEPROM location to read from.

Returns

The data read from EEPROM or an error code (int). To distinguish error values from valid data, error values are returned as negative numbers. See the Arduino Wire.endTransmission() function for a description of return codes. Returns a status of EEPROM_ADDR_ERR if the I/O would extend past the top of the EEPROM address space.

Example
int myData;
//read a byte from location 42
int readValue = myEEPROM.read(42);
if ( readValue < 0 ) {
    //there was a problem
    if ( -readValue == EEPROM_ADDR_ERR) {
        //bad address
    }
    else {
        //some other I2C error
    }
}
else {
    //data read ok
}