WE256K8-200CMA Просмотр технического описания (PDF) - White Electronic Designs => Micro Semi

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WE256K8-200CMA

512Kx8 BIT CMOS EEPROM MODULE

White Electronic Designs => Micro Semi 

White Electronic Designs

WE512K8, WE256K8,

WE128K8-XCX

FIGURE 11 –

SOFTWARE BLOCK DATA

PROTECTION DISABLE ALGORITHM

LOAD DATA AA

TO

ADDRESS 5555

LOAD DATA 55

TO

ADDRESS 2AAA

LOAD DATA 80

TO

ADDRESS 5555

LOAD DATA AA

TO

ADDRESS 5555

LOAD DATA 55

TO

ADDRESS 2AAA

LOAD DATA 20

TO

ADDRESS 5555

LOAD DATA XX

TO

ANY ADDRESS(4)

LOAD LAST BYTE

TO

LAST ADDRESS

(1)

EXIT DATA

PROTECT STATE(3)

NOTES:

1. Data Format: I/O7-0 (Hex);

Address Format: A14 -A0 (Hex).

A17 and A18 control selection of one of four blocks in the 512Kx8.

A15, A16, and A17 control selection of one of 8 pages in the 256Kx8.

A15 and A16 control one of the four blocks in the 128Kx8.

2. Write Protect state will be activated at end of write even if no other data is

loaded.

3. Write Protect state will be deactivated at end of write period even if no other

data is loaded.

4. 1 to 128 bytes of data at each of 4 blocks may be loaded in the 512Kx8.

1 to 64 bytes of data at each of 8 blocks may be loaded in the 256Kx8 and

1 to 64 bytes on 4 blocks in the 128Kx8.

SOFTWARE DATA PROTECTION

A software write protection feature may be enabled

or disabled by the user. When shipped by White

Microelectronics, the devices have the feature disabled.

Write access to the device is unrestricted.

To enable software write protection, the user writes three

access code bytes to three special internal locations.

Once write protection has been enabled, each write to the

EEPROM must use the same three byte write sequence

to permit writing. After setting software data protection,

any attempt to write to the device without the three-byte

command sequence will start the internal write timers. No

data will be written to the device, however, for the duration

of tWC. The write protection feature can be disabled by

a six byte write sequence of specific data to specific

locations. Power transitions will not reset the software

write protection.

Each 32K byte block (128K bytes for the WE512K8)

of EEPROM has independent write protection. One or

more blocks may be enabled and the rest disabled in any

combination. The software write protection guards against

inadvertent writes during power transitions or unauthorized

modification using a PROM programmer. The block

selection is controlled by the upper most address lines

(A17 through A18 for the WE512K8, A15 through A17 for the

WE256K8, or A15 and A16 for the WE128K8).

HARDWARE DATA PROTECTION

Several methods of hardware data protection have been

implemented in the White Microelectronics EEPROM.

These are included to improve reliability during normal

operations.

a) VCC power on delay

As VCC climbs past 3.8V typical the device will wait

5mSec typical before allowing write cycles.

b) VCC sense

While below 3.8V typical write cycles are inhibited.

c) Write inhibiting

Holding OE# low and either CS# or WE# high

inhibits write cycles.

d) Noise filter

Pulses of <8ns (typ) on WE# or CS# will not initiate

a write cycle.

White Electronic Designs Corp. reserves the right to change products or specifications without notice.

May 2000

Rev. 1

11

White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com

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