X88064 Datasheet, PDF (8/15 Pages) Xicor Inc. – E2 Micro-Peripheral

X88064
Block Lock Write Control
The X88064 provides a secondary level of data security
referred to as Block Lock Control. This is accessed
through an extension of the SDP command sequence.
Block Lock allows the user to inhibit writes to any 1K x 8
blocks of memory. Unlike SDP which prevents inadvert-
ent writes, but still allows easy system access to writing
the memory, Block Lock will inhibit all attempts unless it is
specifically disabled by the host. This could be used to
set a higher level of protection in a system where a por-
tion of the memory is used for Program Storage and
another portion is used as Data Storage.
Setting write lockout is accomplished by writing a five-
byte command sequence, opening access to the Block
Lock Register (BLR). After the fifth byte is written, the
user writes to the BLR, selecting which blocks to protect
or unprotect. All write operations, both the command
sequence and writing the data to the BLR, must conform
to the page write timing requirements.
Block Lock Register Format
MSB
LSB
7 65 43 2 1 0
1 = Locked, 0 = Unlocked
BLOCK
ADDRESS
0000–03FF
0400–07FF
0800–0BFF
0C00–0FFF
1000–13FF
1400–17FF
1800–1BFF
1C00–1FFF
7023 FRM F07
Setting Block Lock Register Sequence
WRITE AA
TO 555
WRITE 55
TO AAA
WRITE A0
TO 555
WRITE AA
TO 555
WRITE C0
TO AAA
WRITE BLR
MASK VALUE TO
XXXX
WAIT t_WC
(BLR SET)
EXIT ROUTINE
7023 FRM F08
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