AM29LV008B datasheet(12/38 Pages) AMD

12 / 38 page

Am29LV008B

P R E L I M I NARY

Temporary Sector Unprotect

This feature allows temporary unprotection of previ-

ously protected sectors to change data in-system. The

Sector Unprotect mode is activated by setting the RE-

SET# pin to VID. During this mode, formerly protected

sectors can be programmed or erased by selecting the

sector addresses. Once VID is removed from the RE-

SET# pin, all the previously protected sectors are

protected again. Figure 2 shows the algorithm, and

Figure 20 shows the timing diagrams, for this feature.

Figure 2.

Temporary Sector Unprotect Operation

Hardware Data Protection

The command sequence requirement of unlock cycles

for programming or erasing provides data protection

against inadvertent writes (refer to Table 5 for com-

mand definitions). In addition, the following hardware

data protection measures prevent accidental erasure

or programming, which might otherwise be caused by

spurious system level signals during VCC power-up

and power-down transitions, or from system noise.

Low VCC Write Inhibit

When VCC is less than VLKO, the device does not ac-

cept any write cycles. This protects data during VCC

power-up and power-down. The command register and

all internal program/erase circuits are disabled, and the

device resets. Subsequent writes are ignored until VCC

is greater than VLKO. The system must provide the

proper signals to the control pins to prevent uninten-

tional writes when VCC is greater than VLKO.

Write Pulse “Glitch” Protection

Noise pulses of less than 5 ns (typical) on OE#, CE# or

WE# do not initiate a write cycle.

Logical Inhibit

Write cycles are inhibited by holding any one of OE# =

VIL, CE# = VIH or WE# = VIH. To initiate a write cycle,

CE# and WE# must be a logical zero while OE# is a

logical one.

Power-Up Write Inhibit

If WE# = CE# = VIL and OE# = VIH during power up, the

device does not accept commands on the rising edge

of WE#. The internal state machine is automatically

reset to reading array data on power-up.

COMMAND DEFINITIONS

Writing specific address and data commands or

sequences into the command register initiates device

operations. Table 5 defines the valid register command

sequences. Writing incorrect address and data

values or writing them in the improper sequence

resets the device to reading array data.

All addresses are latched on the falling edge of WE# or

CE#, whichever happens later. All data is latched on

the rising edge of WE# or CE#, whichever happens

first. Refer to the appropriate timing diagrams in the

“AC Characteristics” section.

Reading Array Data

The device is automatically set to reading array data

after device power-up. No commands are required to

retrieve data. The device is also ready to read array

data after completing an Embedded Program or

Embedded Erase algorithm.

After the device accepts an Erase Suspend command,

the device enters the Erase Suspend mode. The

system can read array data using the standard read

timings, except that if it reads at an address within

erase-suspended sectors, the device outputs status

data. After completing a programming operation in the

Erase Suspend mode, the system may once again

read array data with the same exception. See “Erase

Suspend/Erase Resume Commands” for more infor-

mation on this mode.

The system must issue the reset command to re-

enable the device for reading array data if DQ5 goes

high, or while in the autoselect mode. See the “Reset

Command” section, next.

START

Perform Erase or

Program Operations

RESET# = VIH

Temporary Sector

Unprotect Completed

(Note 2)

RESET# = VID

(Note 1)

Notes:

1. All protected sectors unprotected.

2. All previously protected sectors are protected once

again.

21524B-5

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