CAT33C804APATE13 datasheet(4/14 Pages) CATALYST

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Preliminary

CAT33C804A

Doc. No. 25044-00 2/98

PASSWORD PROTECTION

The CAT33C804A is a 4K-bit E2PROM that features a

password protection scheme to prevent unauthorized

access to the information stored in the device. It contains

an access code register which stores one to eight bytes

of access code along with the length of that access code.

Additionally, a memory pointer register stores the ad-

dress that partitions the memory into protected and

unprotected areas. As shipped from the factory, the

device is unprogrammed and unprotected. The length of

the access code is equal to zero and the memory pointer

is fully accessible without an access code. Setting a

password and moving the memory pointer register to

cover all or part of the memory secures the device. Once

secured, the memory is divided into a read/write area

and a read-only area with the entry of a valid access

code. If no access code is entered, the memory is

divided into a read-only area and a non-access area.

Figure 2 illlustrates this partitioning of the memory array.

WRITE PROTECTION

Another feature of the CAT33C804A is WRITE-protec-

tion without the use of an access code. If the memory

pointer register is set to cover all or part of the memory,

without setting the access code register, the device may

be divided into an area which allows full access, and an

area which allows READ-only access. To write into the

READ-only area, the user can override the memory

pointer register for every WRITE instruction or he can

simply move the address in the memory pointer register

to uncover this area, and then write into the memory.

This mechanism prevents inadvertent overwriting of

important data in the memory without the use of an

access code. Figure 3 illustrates this partitioning of the

memory array.

Figure 1. A.C. Timing

Note:

(1) If PE pin = 1.

33C804 F03

VCC

CLK

tVCCS

HIGH-Z

START BIT

STOP BIT

HIGH-Z

tHZ

DATA TIMING

MARK

SPACE

BIT TIME

104

µs

(1)

CHARACTER TIME @ 9600 BAUD

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