EC24C128A/256A

128K/256K-bit 2-WIRE SERIAL CMOS EEPROM

Page 8 of 16

3I23N-Rev.F002

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 "1". 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, increased 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 byte of the first page. The address "roll

over" during write is from the last byte of the current page to the first byte of the same page.

Once the device address with the read/write select bit set to "1" is clocked in and acknowledged by the

EEPROM, the current address data word is serially clocked out. The microcontroller does not respond with an

input "0" but does generate a following stop condition (see to Figure 7).

RANDOM READ: A random read requires a "dummy" byte write sequence to load in the data word address.

Once the device address word and data word address are clocked in and acknowledged by the EEPROM, the

microcontroller must generate another start condition. The microcontroller now initiates a current address read

by sending a device address with the read/write select bit high. The EEPROM acknowledges the device

address and serially clocks out the data word. The microcontroller does not respond with a "0" but does

generate a following stop condition (see to Figure 8).

SEQUENTIAL READ: Sequential reads are initiated by either a current address read or a random address

read. After the microcontroller receives a data word, it responds with an acknowledge. As long as the

EEPROM receives an acknowledge, it will continue to increment the data word address and serially clock out

sequential data words. When the memory address limit is reached, the data word address will "roll over" and

the sequential read will continue. The sequential read operation is terminated when the microcontroller does

not respond with a "0" but does generate a following stop condition (see to Figure 9).