11

Atmel AT24C128C [DATASHEET]

8734B–SEEPR–9/2012

9.

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



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 one 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 zero but does

generate a following stop condition (See Figure 9-1).

Figure 9-1. 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 zero but does generate a following stop condition. (See Figure 9-2)

Figure 9-2. Random Read

Note:

* = Don’t care bit

SDA Line

S

T

A

R

T

Device

Address

R

E

A

D

S

T

O

P

M

S

B

A

C

K

R

/

W

N

O

A

C

K

Data

SDA LINE

S

T

A

R

T

S

T

A

R

T

R

E

A

D

W

R

I

T

E

S

T

O

P

Device

Address

Second Word

Address

Device

Address

First Word

Address

Data (n)

M

S

B

A

C

K

A

C

K

A

C

K

L

S

B

A

C

K

N

O

A

C

K

R

/

W

Dummy Write

R

/

W