AVR Embedded Tutorial - I²C EEPROM
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I²C EEPROM (24LC256)
This code is for an Atmega328 / Arduino with a 16MHz clock and an 24LC256 I2C compatible 2-wire Serial EEPROM. Other 24LCxx EEPROMs can also be controlled.
The following functions are described in other tutorials:
This tutorial shows you how to control an external EEPROM (24LC256) which is connected to the I²C bus.
PullUp resistors are necessary, the EEPROM does not contain any itself.
Functions for EEPROM (24LC256) control
Constants
const
TWI_Write = 0;
TWI_Read = 1;Functions
Note: For a ShortString, the length byte is stored at position [0] in the string.
Call parameters:
- addr device address on the I²C bus
- pos storage location in the EEPROM
- value byte to be written
Functions for writing and reading a byte
// Write a character
procedure I2C_EEPROM_Write(addr , pos : Int16; value : Byte);
begin
TWIStart((addr shl 1) or TWI_Write);
TWIWrite(pos shr 8);
TWIWrite(pos and $FF);
TWIWrite(value);
TWIStop;
delay_ms(10);
end;
// Read a character
function I2C_EEPROM_Read(addr, pos : Int16) : byte;
begin
TWIStart((addr shl 1) or TWI_Write);
TWIWrite(pos shr 8);
TWIWrite(pos and $FF);
TWIStop;
TWIStart((addr shl 1) or TWI_Read);
Result := TWIReadNACK;
TWIStop;
end;Functions for writing and reading a string
A ShortString, or other buffer, is written / read character by character.
// Write a string, including length byte
procedure I2C_EEPROM_WriteString(addr, pos : Int16; s : ShortString);
var
i : byte;
begin
for i := 0 to Length(s) do
begin
I2C_EEPROM_Write(addr, pos + i, byte(s[i]));
end;
end;
// Read a string, including length byte
function I2C_EEPROM_ReadString(addr, pos : Int16) : ShortString;
var
i, l : byte;
begin
l := I2C_EEPROM_Read(addr, pos); // read length of string stored at [0]
SetLength(Result, l);
for i := 1 to l do
begin
Result[i] := Char(I2C_EEPROM_Read(addr, pos + i));
end;
end;Example program
Constants and variables
const
I2Caddr = $54; // Address of the 24LC256 on the I²C bus
s1 = 'Hello World!';
s2 = 'AVR with Lazarus is so beautiful';
var
s : ShortString;Main program
Since a ShortString is 256 bytes long, the second string at address $100 (256) is saved in the EEPROM.
begin
UARTInit; // initialize UART
TWIInit; // initialize I²C
asm Sei END; // enable interrupts
// save the two strings
I2C_EEPROM_WriteString(I2Caddr, 0, s1); // first string
I2C_EEPROM_WriteString(I2Caddr, $100, s2); // second string
// eeload the strings for verification
repeat
s := I2C_EEPROM_ReadString(I2Caddr, 0);
UARTSendString('s1:');
UARTSendString(s);
UARTSendString(#13#10);
s := I2C_EEPROM_ReadString(I2Caddr, $100);
UARTSendString('s2:');
UARTSendString(s);
UARTSendString(#13#10);
until 1 = 2;
end.If you do not believe that the string is in the EEPROM, you can exclude the two lines with WriteString (... and test again.
See also
- Overview page - AVR Embedded Tutorials
From the Free Pascal wiki, page "AVR Embedded Tutorial - I²C EEPROM", as it stood on 2020-03-08 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.
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