AT24C256C_09 Datasheet, PDF (9/21 Pages) ATMEL Corporation – Two-wire Serial EEPROM

AT24C256C [Preliminary]
4. Device Addressing
The 256K EEPROM requires an 8-bit device address word following a start condition to enable the chip for a read or
write operation (refer to Figure 8). The device address word consists of a mandatory “1”, “0” sequence for the first four
most significant bits as shown. This is common to all two-wire EEPROM devices.
Figure 8. Device Addressing
1
0
1
0
A2
A1
A0
R/W
MSB
LSB
The next three bits are the A2, A1, A0 device address bits to allow as many as eight devices on the same bus. These
bits must compare to their corresponding hardwired input pins. The A2, A1, and A0 pins use an internal proprietary
circuit that biases them to a logic low condition if the pins are allowed to float.
The eighth bit of the device address is the read/write operation select bit. A read operation is initiated if this bit is high,
and a write operation is initiated if this bit is low.
Upon a compare of the device address, the EEPROM will output a “0”. If a compare is not made, the device will return
to a standby state.
DATA SECURITY: The AT24C256C has a hardware data protection scheme that allows the user to write protect the
whole memory when the WP pin is at V_CC.
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8568A–SEEPR–9/09