11

5279C–SEEPR–3/09

AT24C256B

7.

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.

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 7-1).

Figure 7-1.

Current Address Read

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 7-2).

Figure 7-2.

Random Read

Note: