The information and code on the playground are for large I2C EEPROMS (24C32 and larger). These have a protocol that has a control byte (device address) and two address bytes (for the EEPROM word address), so the EEPROM word address can be 16 bits long
The smaller EEPROMS have a protocol that use a control byte and only one address byte. For devices larger than 256 bytes (i.e. larger than 24C02), the upper address bits are stuffed into the lower bits of the control byte (the first byte in the transfer).
Here's a demonstration that I worked up for a colleague who was reading and writing some 24C04 devices. I created a few functions that I thought might be useful. The bottom line is that if you can read a single byte and you can write a single byte, you can expand to more elegant functions in any way that seems useful to you. The functions can be incorporated into a library if you are going to write different applications using them, but for testing I find that it's more convenient to have them in the main sketch.
[/begin disclaimer]
These few functions have been tested (somewhat) on 24C02 and 24C04 devices. As far as I know, they are "safe," to the hardware (assuming you are using 5 Volt devices) and they should work for all small I2C EEPROMS up to and including the 24C16 or equivalent.
Bottom line: IWFMYMMV (It Works For Me: Your Mileage May Vary)
---davekw7x
[/end disclaimer]
Regards,
Dave
/*
* Use the I2C bus with small EEPROMs
* 24C01, 20C02, 24C04, 24C08, 24C16
* Sketch: I2C_EEPROM_Small.pde
*
* Derived from sketch for 24C64 devices posted on
* http://www.arduino.cc/playground/Code/I2CEEPROM
* From hkhijhe Date: 01/10/2010
*
* This one by davekw7x
* March, 2011
*
* For a single device, connect as follows:
* EEPROM 4 (GND) to GND
* EEPROM 8 (Vcc) to Vcc (5 Volts)
* EEPROM 5 (SDA) to Arduino Analog Pin 4
* EEPROM 6 (SCL) to Arduino Analog Pin 5
* EEPROM 7 (WP) to GND
* EEPROM 1 (A0) to GND
* EEPROM 2 (A1) to GND
* EEPROM 3 (A2) to GND
*/
#include <Wire.h>
// The seven-bit device address for EEPROMs
// I'll define it here rather than hard-code it inside all of the
// functions.
//
const byte DEVADDR = 0x50;
void setup()
{
byte msg1[] = "Message 1."; // data to write
byte msg2[] = "Zaphod says yo";
byte msg3[] = "Tttthat's all, folks!";
byte msgf[16] = {
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
};
Wire.begin();
Serial.begin(9600);
//
// Change #if 0 to #if 1 and it will erase the
// EEPROM pages that we are going to write to:
//
#if 0
eeprom_write_page(DEVADDR, 0x000, msgf, 16);
eeprom_write_page(DEVADDR, 0x010, msgf, 16);
eeprom_write_page(DEVADDR, 0x020, msgf, 16);
eeprom_write_page(DEVADDR, 0x100, msgf, 16);
eeprom_write_page(DEVADDR, 0x1f0, msgf, 16);
Serial.println("After erasing pages starting at 0x000, 0x100, and 0x1f0:");
eeprom_dump(DEVADDR, 0, 512);
#endif
//
// Change #if 1 to #if 0 so that it won't write over the stuff next time
//
#if 1
// Write some stuff to EEPROM
eeprom_write_page(DEVADDR, 0x000, msg1, sizeof(msg1));
eeprom_write_page(DEVADDR, 0x100, msg2, sizeof(msg2));
eeprom_write_page(DEVADDR, 0x1f0, msg3, 16);
#endif
Serial.println("Memory written");
}
void loop()
{
//
// Read the first page in EEPROM memory, a byte at a time
//
Serial.println("eeprom_read_byte, starting at 0");
for (int i = 0; i < 16; i++) {
byte b = eeprom_read_byte(DEVADDR, i);
Serial.print(b, HEX);
Serial.print(' ');
}
Serial.println();
//
// Read the first page using the read_buffer function
//
Serial.println("eeprom_read_buffer, starting at 0");
byte buffer[16];
eeprom_read_buffer(DEVADDR, 0, buffer, sizeof(buffer));
//
//First print the hex bytes on this row
//
for (int i = 0; i < sizeof(buffer); i++) {
char outbuf[6];
sprintf(outbuf, "%02X ",buffer[i]);
Serial.print(outbuf);
}
Serial.println();
//
// Now print the char if printable ASCII
// otherwise print '.'
//
for (int i = 0; i < sizeof(buffer); i++) {
if (isprint(buffer[i])) {
Serial.print(buffer[i]);
}
else {
Serial.print('.');
}
}
Serial.println();
// Now dump 512 bytes
Serial.println("eeprom_dump(DEVADDR, 0, 512)");
eeprom_dump(DEVADDR, 0, 512);
Serial.println();
delay(20000);
}
void eeprom_write_byte(byte deviceaddress, int eeaddress, byte data)
{
// Three lsb of Device address byte are bits 8-10 of eeaddress
byte devaddr = deviceaddress | ((eeaddress >> 8) & 0x07);
byte addr = eeaddress;
Wire.beginTransmission(devaddr);
Wire.send(int(addr));
Wire.send(int(data));
Wire.endTransmission();
delay(10);
}
// Pages are blocks of 16 bytes, starting at 0x000.
// That is, pages start at 0x000, 0x010, 0x020, ...
// For a device "page write", the last byte must be
// on the same page as the first byte.
//
// No checking is done in this routine.
//
// TODO: Do some checking, or, better yet (maybe)
// make length an int and do repeated device
// page writes if necessary. (Then maybe rename to
// eeprom_write_pages or some such thing.)
//
void eeprom_write_page(byte deviceaddress, unsigned eeaddr,
const byte * data, byte length)
{
// Three lsb of Device address byte are bits 8-10 of eeaddress
byte devaddr = deviceaddress | ((eeaddr >> 8) & 0x07);
byte addr = eeaddr;
Wire.beginTransmission(devaddr);
Wire.send(int(addr));
for (int i = 0; i < length; i++) {
Wire.send(data[i]);
}
Wire.endTransmission();
delay(10);
}
// TODO: Change to integer data type and return -1 if can't
// read.
//
int eeprom_read_byte(byte deviceaddress, unsigned eeaddr)
{
byte rdata = -1;
// Three lsb of Device address byte are bits 8-10 of eeaddress
byte devaddr = deviceaddress | ((eeaddr >> 8) & 0x07);
byte addr = eeaddr;
Wire.beginTransmission(devaddr);
Wire.send(int(addr));
Wire.endTransmission();
Wire.requestFrom(int(devaddr), 1);
if (Wire.available()) {
rdata = Wire.receive();
}
return rdata;
}
//
// Returns number of bytes read from device
//
// Due to buffer size in the Wire library, don't read more than 30 bytes
// at a time! No checking is done in this function.
//
// TODO: Change length to int and make it so that it does repeated
// EEPROM reads for length greater than 30.
int eeprom_read_buffer(byte deviceaddr, unsigned eeaddr,
byte * buffer, byte length)
{
// Three lsb of Device address byte are bits 8-10 of eeaddress
byte devaddr = deviceaddr | ((eeaddr >> 8) & 0x07);
byte addr = eeaddr;
Wire.beginTransmission(devaddr);
Wire.send(int(addr));
Wire.endTransmission();
Wire.requestFrom(devaddr, length);
int i;
for (i = 0; i < length && Wire.available(); i++) {
buffer[i] = Wire.receive();
}
return i;
}
//
// The display is like hexdump -C. It will always
// begin and end on a 16-byte boundary.
//
void eeprom_dump(byte devaddr, unsigned addr, unsigned length)
{
// Start with the beginning of 16-bit page that contains the first byte
unsigned startaddr = addr & (~0x0f);
// stopaddr is address of next page after the last byte
unsigned stopaddr = (addr + length + 0x0f) & (~0x0f);
for (unsigned i = startaddr; i < stopaddr; i += 16) {
byte buffer[16]; // Hold a page of EEPROM
char outbuf[6]; //Room for three hex digits and ':' and ' ' and '\0'
sprintf(outbuf, "%03x: ", i);
Serial.print(outbuf);
eeprom_read_buffer(devaddr, i, buffer, 16);
for (int j = 0; j < 16; j++) {
if (j == 8) {
Serial.print(" ");
}
sprintf(outbuf, "%02x ", buffer[j]);
Serial.print(outbuf);
}
Serial.print(" |");
for (int j = 0; j < 16; j++) {
if (isprint(buffer[j])) {
Serial.print(buffer[j]);
}
else {
Serial.print('.');
}
}
Serial.println("|");
}
}
