CAT28HT256

8-99

Advanced

Stock No. 21065-03 2/98

To activate the software data protection, the device must

be sent three write commands to specific addresses with

specific data (Figure 9). This sequence of commands

(along with subsequent writes) must adhere to the page

write timing specifications (Figure 11). Once this is done,

all subsequent byte or page writes to the device must be

preceded by this same set of write commands. The data

protection mechanism is activated until a deactivate

sequence is issued regardless of power on/off transi-

tions. This gives the user added inadvertent write pro-

tection on power-up in addition to the hardware protec-

tion provided.

To allow the user the ability to program the device with

is a software command sequence for deactivating the

data protection. The six step algorithm (Figure 10) will

reset the internal protection circuitry, and the device will

return to standard operating mode (Figure 12 provides

reset timing). After the sixth byte of this reset sequence

has been issued, standard byte or page writing can

commence.

Figure 11. Software Data Protection Timing

5096 FHD F13

CE

WE

tWP

AA

5555

55

2AAA

A0

5555

DATA

ADDRESS

tBLC

tWC

BYTE OR

PAGE

WRITES

ENABLED

Figure 12. Resetting Software Data Protection Timing

CE

WE

AA

5555

55

2AAA

DATA

ADDRESS

tWC

80

5555

AA

5555

55

2AAA

20

5555

SDP

RESET

DEVICE

UNPROTECTED

5096 FHD F14

ORDERING INFORMATION

Notes:

(1)

The device used in the above example is a CAT28HT256HD-20 (100,000 Cycle Endurance, CERDIP, 200 ns Access Time).

28HT256 F16

Speed

20: 200ns

25: 250ns

Prefix

Device #

Suffix

28HT256

Product

Number

CAT

Optional

Company

ID

-20

Package

D: CERDIP

D

H

Endurance

Blank = 10,000 Cycle

H = 100,000 Cycle