X68C64 Datasheet, PDF (6/12 Pages) Xicor Inc. – E2 Micro-Peripheral

X68C64
DATA PROTECTION
The X68C64 provides two levels of data protection
through software control. There is a global software data
protection feature similar to the industry standard for
E²PROMs and a new Block Protect write lockout protec-
tion providing a secondary level of data security.
Writing with SDP
WRITE AA
TO X555
WRITE 55
TO XAAA
PERFORM BYTE
OR PAGE WRITE
OPERATIONS
WAIT tWC
WRITE A0
TO X555
EXIT ROUTINE
X = A₁₂:
A₁₂ = 1 IF DATA TO BE WRITTEN IS WITHIN
ADDRESS 1000 TO 1FFF.
A₁₂ = 0 IF DATA TO BE WRITTEN IS WITHIN
ADDRESS 0000 TO 0FFF.
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Software Data Protection
Software Data Protection (SDP) is employed to protect
the entire array against inadvertent writes. To write to
the X68C64, a three-byte command sequence must
precede the byte(s) being written.
All write operations, both the command sequence and
any data write operations, must conform to the page
write timing requirements.
Block Protect Write Lockout
The X68C64 provides a secondary level of data security
referred to as Block Protect write lockout. This is ac-
cessed through an extension of the SDP command
sequence. Block Protect allows the user to lockout
writes to any 1K x 8 blocks of memory. Unlike SDP which
prevents inadvertent writes, but still allows easy system
access to writing the memory, Block Protect will lockout
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 portion 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
Protect Register (BPR). After the fifth byte is written, the
user writes to the BPR, selecting which blocks to protect
or unprotect. All write operations, both the command
sequence and writing the data to the BPR, must conform
to the page write timing requirements.
Block Protect Register Format
MSB
LSB
7654321 0
BLOCK
ADDRESS
0000–03FF
0400–07FF
0800–0BFF
0C00–0FFF
1000–13FF
1400–17FF
1800–1BFF
1C00–1FFF
1 = Protect, 0 = Unprotect Block Specified
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Setting BPR Command Sequence
WRITE AA
TO X555
WRITE C0
TO XAAA
WRITE 55
TO XAAA
WRITE A0
TO X555
WRITE BPR
MASK VALUE TO
ANY ADDRESS
WAIT tWC
WRITE AA
TO X555
EXIT ROUTINE
X = A₁₂:
A₁₂ = 1 IF PROGRAM BEING EXECUTED IS
WITHIN 0000 TO 0FFF.
A₁₂ = 0 IF PROGRAM BEING EXECUTED
RESIDES WITHIN 1000 TO 1FFF.
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