AT34C02

8

Figure 1. Setting Write Protect Register

Read Operations

Read operations are initiated the same way as write opera-

tions 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 dur-

ing 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. To end

the command, the microcontroller does not respond with an

input zero but does generate a following stop condition

(refer to Figure 5).

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. To end the command, the microcontroller

does not respond with a zero but does generate a following

stop condition (refer to Figure 6).

WP Connected to GND or Floating

Start

R/W Bit

Write Protect Register

Acknowledgment

from Device

Action from Device

1010

R

X

ACK

Read Array

1010

W

Programmed

ACK

Can Write to First Half Only

1010

W

Not Programmed

ACK

Can Write to Full Array

0110

R

Programmed

No ACK

Stop - Indicates Write Protect Register is Programmed

0110

R

Not Programmed

ACK

Read Out Data Don’t Care. Indicates WP Register is Not Prog

0110

W

Programmed

No ACK

Stop - Indicates Write Protect Register is Programmed

0110

W

Not Programmed

ACK

Program Write Protect Register (irreversible)

WP Connected to V

CC

1010

R

X

ACK

Read Array

1010

W

Programmed

ACK

Device Write Protect

1010

W

Not Programmed

ACK

Device Write Protect

0110

R

Programmed

No ACK

Stop - Indicates Write Protect Register is Programmed

0110

R

Not Programmed

ACK

Read Out Data Don’t Care. Indicates WP Register is Not Prog

0110

W

Programmed

No ACK

Stop - Indicates Write Protect Register is Programmed

0110

W

Not Programmed

ACK

Cannot Program Write Protect Register

S

T

A

R

T

S

T

O

P

SDA LINE

WORD

ADDRESS

DATA

CONTROL

BYTE

A

C

K

01 1 0

0

A

C

K

A

C

K