ACE24LA128A

Two-wire Serial EEPROM

VER 1.1

8

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, 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

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 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 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 Figure9).

Read Identification Page:

The Identification Page (64 bytes) is an additional page which can be written and (later) permanently

locked in Read-only mode.

The Identification Page can be read by issuing an Read Identification Page instruction. This instruction

uses the same protocol and format as the Random Address Read (from memory array) with device type

identifier defined as 1011b. The MSB address bits B15/B6 are don't care, the LSB address bits B5/B0

define the byte address inside the Identification Page. The number of bytes to read in the ID page must

not exceed the page boundary (e.g.: when reading the Identification Page from location 10d, the number

of bytes should be less than or equal to 22, as the ID page boundary is 64 bytes)