9

AT24C01B [Preliminary]

5156B–SEEPR–5/06

Device Addressing

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

tion to enable the chip for a read or write operation (refer to Figure 7).

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

most significant 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 opera-

tion 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 zero. If a compare is

not made, the chip will return to a standby state.

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 condi-

tion. At this time the EEPROM enters an internally timed write cycle, t

nonvolatile memory. All inputs are disabled during this write cycle and the EEPROM will

not respond until the write is complete (see Figure 8 on page 11).

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 terminate the page write sequence with a stop condition (see Fig-

ure 9 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 following 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 send-

ing 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.

Read Operations

Read operations are initiated the same way as write operations with the exception that

the read/write select bit in the device address word is set to one. There are three read

operations: current address read, random address read and sequential read.

CURRENT ADDRESS READ: The internal data word address counter maintains the

last address accessed during the last read or write operation, incremented by one. This

address stays valid between operations as long as the chip power is maintained. The

address “roll over” during read is from the last byte of the last memory page to the first