AM29F032B datasheet(14/39 Pages) AMD

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Am29F032B

Hardware Data Protection

The command sequence requirement of unlock cycles

for programming or erasing provides data protection.

In addition, the following hardware data protection

measures prevent accidental erasure or programming,

which might otherwise be caused by spurious system

level signals during V

CC power-up and power-down

transitions, or from system noise.

Low VCC Write Inhibit

When V

CC is less than VLKO (see DC Characteristics

for voltage levels), the device does not accept any

write cycles. This protects data during V

CC power-up

and power-down. The command register and all inter-

nal program/erase circuits are disabled. Under this

condition the device resets to the read mode. Subse-

quent writes are ignored until the V

CC level is greater

than V

LKO. The system must ensure that the control

pins are logically correct to prevent unintentional

writes when V

CC is above 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# =

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

CE# and WE# must be at V

IL while OE# is at VIH.

Power-Up Write Inhibit

If WE# = CE# = V

IL and OE# = VIH during power up,

the device does not accept commands on the rising

edge of WE#. The internal state machine is automati-

cally reset to the read mode on power-up.

COMMAND DEFINITIONS

Writing specific address and data commands or se-

quences into the command register initiates device op-

erations. The Command Definitions table defines the

valid register command sequences. Writing incorrect

address and data values or writing them in the im-

proper 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 command,

the device enters the Erase Suspend mode. The sys-

tem can read array data using the standard read tim-

ings, 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-en-

able the device for reading array data if DQ5 goes

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

Command” section, next.

See also “Requirements for Reading Array Data” in

the “Device Bus Operations” section for more informa-

tion. The Read Operations table provides the read pa-

rameters, and Read Operation Timings diagram

shows the timing diagram.

Reset Command

Writing the reset command to the device resets the

device to reading array data. Address bits are don’t

care for this command.

The reset command may be written between the se-

quence cycles in an erase command sequence before

erasing begins. This resets the device to reading array

data. Once erasure begins, however, the device ig-

nores reset commands until the operation is complete.

The reset command may be written between the se-

quence cycles in a program command sequence be-

fore programming begins. This resets the device to

reading array data (also applies to programming in

Erase Suspend mode). Once programming begins,

however, the device ignores reset commands until the

operation is complete.

The reset command may be written between the se-

quence cycles in an autoselect command sequence.

Once in the autoselect mode, the reset command

must be written to return to reading array data (also

applies to autoselect during Erase Suspend).

If DQ5 goes high during a program or erase operation,

writing the reset command returns the device to read-

ing array data (also applies during Erase Suspend).

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