X24128
Table 1. Block Lock Protect Bits and Protected Addresses
BL1
BL0
Protected Addresses
None
Array Location
No Protect
Upper 1/4
0
0
1
1
0
1
0
1
3000h–3FFFh
2000h–3FFFh
0000h–3FFFh
Upper 1/2
Full Array
Table 2. WP Pin and WPEN Bit Functionality
Memory Array Not
Memory Array Block
Lock Protected
WP
WPEN
Lock Block Protected
Block Lock Bits
WPEN Bit
Unprotected
Unprotected
Protected
0
X
0
1
Unprotected
Protected
Protected
Protected
Unprotected
Unprotected
Protected
X
Unprotected
1
Unprotected
Writing to the WEL and RWEL bits
3) Set BL1, BL0, and/or WPEN bits, Write u00xy010 to
address FFFFh, where u = WPEN, x = BL1, and y =
BL0. (Nonvolatile Write Cycle.)
WEL and RWEL are volatile latches that power up in
the LOW (disabled) state. While the WEL bit is LOW,
writes to any address other than FFFFh will be ignored
(no acknowledge will be issued after the Data Byte).
The WEL bit is set by writing 00000010 to address
FFFFh. Once set, WEL remains HIGH until either it is
reset to 0 (by writing 00000000 to FFFFh) or until the part
powers up again. Writes to WEL and RWEL do not cause
a nonvolatile write cycle, so the device is ready for the
next operation immediately after the stop condition.
The three step sequence was created to make it diffi-
cult to change the contents of the Write Protect Regis-
ter accidentally. If WEL was set to one by a previous
register write operation, the user may start at step 2.
RWEL is reset to zero in step 3 so that user is required
to perform steps 2 and 3 to make another change.
RWEL must be 0 in step 3. If the RWEL bit in the data
byte for step 3 is a one, then no changes are made to
the Write Protect Register and the device remains at
step 2.
The RWEL bit controls writes to the Block Lock protect
bits, BL0 and BL1, and the WPEN bit. If RWEL is 0
then no writes can be performed on BL0, BL1, or
WPEN. RWEL is reset when the device powers up or
after any nonvolatile write, including writes to the Block
Lock protect bits, WPEN bit, or any bytes in the mem-
ory array. When RWEL is set, WEL cannot be reset,
nor can RWEL and WEL be reset in one write opera-
tion. RWEL can be reset by writing 00000010 to
FFFFh; but this is the same operation as in step 3
described below, and will result in programing BL0,
BL1, and WPEN.
The WP pin must be LOW or the WPEN bit must be
LOW before a nonvolatile register write operation is ini-
tiated. Otherwise, the write operation will abort and the
device will go into standby mode after the master
issues the stop condition in step 3.
Step 3 is a nonvolatile write operation, requiring t
to
WC
complete (acknowledge polling may be used to reduce
this time requirement). It should be noted that step 3
MUST end with a stop condition. If a start condition is
issued during or at the end of step 3 (instead of a stop
condition) the device will abort the nonvolatile register
write and remain at step 2. If the operation is aborted
with a start condition, the master must issue a stop to
put the device into standby mode.
Writing to the BL and WPEN Bits
A 3 step sequence is required to change the nonvola-
tile Block Lock protect or Write Protect Enable bits:
1) Set WEL = 1, Write 00000010 to address FFFFh
(Volatile Write Cycle.)
2) Set RWEL = 1, Write 00000110 to address FFFFh
(Volatile Write Cycle.)
Characteristics subject to change without notice. 9 of 16
REV 1.1 9/8/00
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