You have a vast sequence of instructions. When all you want to do is write '_DATA' to location 0x1111 in the 24C256. And just to make it more incomprehensible, you have chosen '_DATA' to have a value of 0x11.

Murray has shown an example for a 24C02. You must do all the I2C commands in the correct order. You have issued a STOP before the READ.

If you write the functions correctly, then you would simply have:

char i2c_write_single_byte_at(char slave, unsigned int address, char value);
char i2c_read_single_byte_at(char slave, unsigned int address);
...
if (i2c_write_single_byte_at(0xA0, 0x1234, 0x56) != OK) { // an error
    ...
value = i2c_write_single_byte_at(0xA0, 0x1234);           // read value

 

You can build your functions from Murray's primitives. Or you may choose to write functions with a 'size' parameter so that you read or write multiple bytes.

David.