I was scanning for a used address by I2C EEPROM (24C02). Contrary to my expectations, it returned all eight possible addresses (0x50-0x57) instead of the hardwired one. I thought the problem was in a faulty chip, but changing to a new one didn't fix the problem.
Is this a "feature"? I hope not, as it would eliminate the purpose of having multiple EEPROMs connected to the same I2C bus. I tried to search on this topic, but only found this:
ATMEL 24C02 EEPROM – Trouble understanding how the addressing works. Sadly, it doesn't answer my question, so I hope someone knows that is going on.
The EEPROM that I am using has markings ATMEL711 24C02 PU24 D.
Edit1:
Here are example waveforms when I am trying to read one byte from EEPROM (hardwired to 0x50):
As you can see, both addresses work (0x50 and 0x53) eventhou hardwired address is 0x50.
Edit2:
Here is the schematic showing how the EEPROM is connect. Pull-up resistors on SDA and SCL lines are present but not shown here.
Best Answer
Got exactly the same behavior on eeprom modules from Banggood. The chips are marked ATMEL719 24C02N PU27 D
24C04 parts, also from Banggood, works normally.
Chips marked ATMEL178 24C256 PU27 D are also strange. They respond to two addresses (i.e. 57 and 5f) and all 3 address select pins will modify the i2c address pair (i.e. 50 to 57 and 58 to 5f).
The genuine chip has just one active address and only use the A0 and A1 pins, according to the data sheet.
Caveat Emptor