Can an I2C Eeprom have two addresses? - arduino

Question

I own an EEPROM module with the P24C256 chip. (not AT24C256).
After scanning for available I2C devices, i got response from two devices.
Scanning...
I2C device found at address 0x50 !
I2C device found at address 0x58 !
done
I looked up the datasheet, but cannot find any additional information.
I thought that the device, has two banks for storage, but that does not seem to be the case.
How is this possible? After disconnecting the module, no I2C devices are reported.
#include <Wire.h>
void setup()
{
Wire.begin();
Serial.begin(9600);
while (!Serial); // Leonardo: wait for serial monitor
Serial.println("\nI2C Scanner");
}
void loop()
{
byte error, address;
int nDevices;
Serial.println("Scanning...");
nDevices = 0;
for(address = 1; address < 127; address++ )
{
// The i2c_scanner uses the return value of
// the Write.endTransmisstion to see if
// a device did acknowledge to the address.
Wire.beginTransmission(address);
error = Wire.endTransmission();
if (error == 0)
{
Serial.print("I2C device found at address 0x");
if (address<16)
Serial.print("0");
Serial.print(address,HEX);
Serial.println(" !");
nDevices++;
}
else if (error==4)
{
Serial.print("Unknown error at address 0x");
if (address<16)
Serial.print("0");
Serial.println(address,HEX);
}
}
if (nDevices == 0)
Serial.println("No I2C devices found\n");
else
Serial.println("done\n");
delay(5000); // wait 5 seconds for next scan
}

Answer 1

Yes they can.
Depending on the size of the i2C EEPROM and how the memory blocks are organized you can have 2 or more device address. For example the ST24/25x04 EEPROM are 4 Kbit electrically erasable programmable memories, organized as 2 blocks of 256 x8 bits. That means that I2C gives you two device addresses (0x50 and 0x51 in the memory above), that will access each block with 1 byte address.

Answer 2

It might be the problem with the EEPROM address bits, in case they are in floating state and not connected properly, Could you please check the connections on those address bits? Try to connect them to the same ground as your micro-controller, but yes, as advised above, schematics is highly needed.

Answer 3

That behavior is not implied to by. The datasheet says the address should be only one (but its three lower bits can be chosen).
The schematics for the boards shows only two bits (A0, A1) are selected by the dip-switch, and A2 is tied to the ground.
I see no initialization in the code. What frequency the TWI bus is working at? Also, in the pictures of the module it has jumpers to pull-up resistors unsoldered, and it has 10kOhm pull-up resistors even if jumpers are soldered - that may be too high.
Probably you have issue just because the wire is not returned to the high level fast enough.
Check pull-up resistors are engaged (jumpers are soldered on the board)
Try to add additional pull-ups (about 4.7k) on SCL, SDA
Try to set lower frequency, e.g. Wire.setClock(50000);