AM29LL800BB-150SCB datasheet(13/40 Pages) AMD

13 / 40 page

Am29LL800B

ADV ANCE

I N FO RMAT I O N

Figure 3.

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 cy-

cle, 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

automat ic ally res e t t o reading array da ta on

power-up.

COMMAND DEFINITIONS

Writing specific address and data commands or se-

quences into the command register initiates device op-

erations. Table 5 defines the valid register command

sequences. Writing incorrect address and data val-

ues 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 Em-

bedded Erase algorithm.

After the device accepts an Erase Suspend com-

mand, 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 opera-

tion 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 information on this mode.

The system must issue the reset command to re-en-

able the device for reading array data if DQ5 goes high,

or while in the autoselect mode. See the “Reset Com-

mand” section, next.

See also “Requirements for Reading Array Data” in the

“Device Bus Operations” section for more information.

The Read Operations table provides the read parame-

ters, and Figure 14 shows the timing diagram.

Reset Command

Writing the reset command to the device resets the de-

vice to reading array data. Address bits are don’t care

for this command.

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.

21518A-5

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