X88064

8

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

Setting Block Lock Register Sequence

6

5

4

3

2

1

0

7

0000–03FF

0400–07FF

0800–0BFF

0C00–0FFF

1000–13FF

1400–17FF

1800–1BFF

1C00–1FFF

BLOCK

ADDRESS

1 = Locked, 0 = Unlocked

MSB

LSB

7023 FRM F07

WRITE AA

TO 555

WRITE BLR

MASK VALUE TO

XXXX

WRITE 55

TO AAA

WRITE C0

TO AAA

(BLR SET)

7023 FRM F08

WRITE AA

TO 555

WRITE A0

TO 555

EXIT ROUTINE