11

AT34C02

0958Q–SEEPR–1/07

Figure 7. Setting Write Protect Register

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 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 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 (see Figure 11 on page 13).

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

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 Second Half (80H - FFH) 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)

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

= Don't Care