9

5156E–SEEPR–10/08

AT24C01B

6.

Device Addressing

The 1K EEPROM device requires an 8-bit device address word following a start condition to

enable the chip for a read or write operation (refer to Figure 8-1).

The device address word consists of a mandatory one, zero sequence for the first four most sig-

nificant bits as shown. This is common to all the EEPROM devices.

The next 3 bits are the A2, A1 and A0 device address bits for the 1K EEPROM. These 3 bits

must compare to their corresponding hard-wired input pins.

The eighth bit of the device address is the read/write operation select bit. A read operation is ini-

tiated 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 zero. If a compare is not

made, the chip will return to a standby state.

7.

Write Operations

BYTE WRITE: A write operation requires an 8-bit data word address following the device

address word and acknowledgment. Upon receipt of this address, the EEPROM will again

respond with a zero and then clock in the first 8-bit data word. Following receipt of the 8-bit data

word, the EEPROM will output a zero and the addressing device, such as a microcontroller,

must terminate the write sequence with a stop condition. At this time the EEPROM enters an

internally timed write cycle, t

write cycle and the EEPROM will not respond until the write is complete (see Figure 8-2 on page

10).

PAGE WRITE: The 1K EEPROM is capable of an 8-byte page write.

A page write is initiated the same as a byte write, but the microcontroller does not send a stop

condition after the first data word is clocked in. Instead, after the EEPROM acknowledges

receipt of the first data word, the microcontroller can transmit up to seven data words. The

EEPROM will respond with a zero after each data word received. The microcontroller must ter-

minate the page write sequence with a stop condition (see Figure 8-3 on page 11).

The data word address lower three bits are internally incremented following the receipt of each

data word. The higher data word address bits are not incremented, retaining the memory page

row location. When the word address, internally generated, reaches the page boundary, the fol-

lowing byte is placed at the beginning of the same page. If more than eight data words are

transmitted to the EEPROM, the data word address will “roll over” and previous data will be

overwritten.

ACKNOWLEDGE POLLING: Once the internally timed write cycle has started and the

EEPROM inputs are disabled, acknowledge polling can be initiated. This involves sending a

start condition followed by the device address word. The read/write bit is representative of the

operation desired. Only if the internal write cycle has completed will the EEPROM respond with

a zero allowing the read or write sequence to continue.