28C256 datasheet(9/10 Pages) CATALYST

9 / 10 page

CAT28C256

Doc. No. 25020-0A 2/98

Note:

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Write protection is activated at this point whether or not any more writes are completed. Writing to addresses must occur within tBLC

Max., after SDP activation.

HARDWARE DATA PROTECTION

The following is a list of hardware data protection fea-

tures that are incorporated into the CAT28C256.

(1) VCC sense provides for write protection when VCC

falls below 3.5V min.

(2) A power on delay mechanism, tINIT (see AC charac-

teristics), provides a 5 to 10 ms delay before a write

sequence, after VCC has reached 3.5V min.

(3) Write inhibit is activated by holding any one of OE

low, CE high or WE high.

(4) Noise pulses of less than 20 ns on the WE or CE

inputs will not result in a write cycle.

SOFTWARE DATA PROTECTION

The CAT28C256 features a software controlled data

protection scheme which, once enabled, requires a data

algorithm to be issued to the device before a write can be

performed. The device is shipped from Catalyst with the

software protection NOT ENABLED (the CAT28C256 is

in the standard operating mode).

Figure 9. Write Sequence for Activating Software

Data Protection

Figure 10. Write Sequence for Deactivating

Software Data Protection

WRITE DATA:

ADDRESS:

5555

WRITE DATA:

ADDRESS:

2AAA

WRITE DATA:

ADDRESS:

5555

WRITE DATA:

ADDRESS:

5555

WRITE DATA:

ADDRESS:

2AAA

WRITE DATA:

ADDRESS:

5555

5096 FHD F08

5096 FHD F09

SOFTWARE DATA

PROTECTION ACTIVATED

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WRITE DATA:

WRITE LAST BYTE

LAST ADDRESS

TO ANY ADDRESS

WRITE DATA:

ADDRESS:

5555

WRITE DATA:

ADDRESS:

2AAA

WRITE DATA:

ADDRESS:

5555

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