X68C64

6

WRITE AA

TO X555

WRITE 55

TO XAAA

WRITE A0

TO X555

PERFORM BYTE

OR PAGE WRITE

OPERATIONS

WAIT tWC

EXIT ROUTINE

X = A

A

ADDRESS 1000 TO 1FFF.

A

ADDRESS 0000 TO 0FFF.

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

tion providing a secondary level of data security.

Writing with SDP

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.

3868 FHD F09

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.

Block Protect Register Format

3868 FHD F11

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 Command Sequence

3868 FHD F12

WRITE AA

TO X555

WRITE BPR

MASK VALUE TO

ANY ADDRESS

WAIT tWC

EXIT ROUTINE

WRITE 55

TO XAAA

WRITE C0

TO XAAA

WRITE AA

TO X555

WRITE A0

TO X555

X = A

A

WITHIN 0000 TO 0FFF.

A

RESIDES WITHIN 1000 TO 1FFF.