CAT25C128/256
to protect quarter of the memory, half of the memory or
the entire memory by setting these bits. Once protected
the user may only read from the protected portion of the
array. These bits are non-volatile.
STATUS REGISTER
The Status Register indicates the status of the device.
TheRDY(Ready)bitindicateswhethertheCAT25C128/
256 is busy with a write operation. When set to 1 a write
cycle is in progress and when set to 0 the device
indicates it is ready. This bit is read only
TheWPEN(WriteProtectEnable)isanenablebitforthe
WP pin. The WPpin and WPEN bit in the status register
control the programmable hardware write protect fea-
ture. Hardware write protection is enabled when WP is
low and WPEN bit is set to high. The user cannot write
tothestatusregister(includingtheblockprotectbitsand
the WPEN bit) and the block protected sections in the
memory array when the chip is hardware write pro-
tected. Only the sections of the memory array that are
not block protected can be written. Hardware write
protection is disabled when either WP pin is high or the
WPEN bit is zero.
The WEL (Write Enable) bit indicates the status of the
writeenablelatch. Whensetto1, thedeviceisinaWrite
Enable state and when set to 0 the device is in a Write
Disablestate. TheWELbit canonlybesetbytheWREN
instruction and can be reset by the WRDI instruction.
The BPO and BP1 (Block Protect) bits indicate which
blocks are currently protected. These bits are set by the
user issuing the WRSR instruction. The user is allowed
STATUS REGISTER
7
6
5
4
3
2
1
0
WPEN
X
X
X
BP1
BP0
WEL
RDY
BLOCK PROTECTION BITS
Status Register Bits
Array Address
Protected
Protection
BP1
BPO
25C128
25C256
None
0
0
1
1
0
1
0
1
None
No Protection
3000-3FFF
2000-3FFF
0000-3FFF
6000-7FFF
4000-7FFF
0000-7FFF
Quarter Array Protection
Half Array Protection
Full Array Protection
WRITE PROTECT ENABLE OPERATION
Protected
Blocks
Unprotected
Blocks
Status
WPEN
WP
X
WEL
Register
0
0
1
1
X
X
0
1
0
1
0
1
Protected
Protected
Protected
Protected
Protected
Protected
Protected
Writable
Protected
Writable
Protected
Writable
Protected
Writable
X
Low
Low
High
High
Protected
Protected
Protected
Writable
Doc. No. 25088-00 1/01
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CATALYST [ CATALYST SEMICONDUCTOR ]
