at34c02b ATMEL Corporation, at34c02b Datasheet - Page 12

• Manufacturer Part Number: at34c02b
• Description: Two-wire Serial Eeprom With Permanent And Reversible Software Write Protect 2k 256 X 8
• Manufacturer: ATMEL Corporation

Table 9. WP Connected to Vcc
Read Operations
12
WP Connected to Vcc
Command
Set PSWP
Set PSWP
Set RSWP
Set RSWP
PSWP
PSWP
RSWP
RSWP
RSWP
RSWP
Read
Read
Read
Read
Clear
Clear
1010
1010
AT34C02B
R/W Bit
W
W
W
W
W
W
W
R
R
R
R
R
Permanent Write
Protect Register
Not Programmed
Not Programmed
Not Programmed
Programmed
Programmed
Programmed
PSWP
X
X
X
X
X
X
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 13 on page 14).
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
Reversible Write
Protect Register
Not Programmed
Not Programmed
Programmed
Programmed
RSWP
X
X
X
X
X
X
X
X
Acknowledgment
from Device
No ACK
No ACK
No ACK
No ACK
No ACK
ACK
ACK
ACK
ACK
ACK
ACK
ACK
Action from Device
Read array
Device Write Protect
STOP - Indicates permanent write protect register is
programmed
Read out data don't care. Indicates PSWP register is
not programmed
STOP - Indicates permanent write protect register is
programmed
Cannot program write protect registers
STOP - Indicates reversible write protect register is
programmed
Read out data don't care. Indicates RSWP register is
not programmed
STOP - Indicates reversible write protect register is
programmed
Cannot program write protect registers
STOP - Indicates permanent write protect register is
programmed
Cannot write to write protect registers
3417E–SEEPR–1/07