X88C64

7

DATA PROTECTION

The X88C64 provides two levels of data protection

through software control. There is a global software data

protection feature similar to the industry standard for

tion providing a secondary level of data security.

SOFTWARE DATA PROTECTION

Software Data Protection (SDP) is employed to protect

the entire array against inadvertent writes. To write to the

X88C64, 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.

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 Write Lockout

The X88C64 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.

Writing with SDP

3867 FHD F10

Block Protect Register Format

3867 FHD F12

6

5

43

2

1

0

7

0000–03FF

0400–07FF

0800–0BFF

0C00–0FFF

1000–13FF

1400–17FF

1800–1BFF

1C00–1FFF

BLOCK

ADDRESS

1 = Protect, 0 = Unprotect Block Specified

MSB

LSB

Setting BPR Sequence

3867 FHD F13

WRITE AA

TO X555

WRITE 55

TO XAAA

WRITE A0

TO X555

PERFORM BYTE

OR PAGE WRITE

OPERATIONS

WAIT tWC

EXIT ROUTINE

X = A

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.

WRITE AA

TO X555

WRITE BPR

MASK VALUE TO

ANY ADDRESS

WAIT tWC

EXIT ROUTINE

WRITE 55

TO XAAA

WRITE C0

TO XAAA

(BPR REGISTER SET)

WRITE AA

TO X555

WRITE A0

TO X555

X = A

A

RESIDES WITHIN ADDRESS 0000 TO 0FFF.

A

RESIDES WITHIN ADDRESS 1000 TO 1FFF.