AM29F017D datasheet(14/44 Pages) SPANSION

14 / 44 page

Am29F017D

pre v io us ly

pr ote c t ed

s e c t o r

g r oups

are

protected again. Figure 1 shows the algorithm, and

the Temporary Sector/Sector Group Unprotect dia-

gram shows the timing waveforms, for this feature.

Figure 1.

Temporary Sector Group Unprotect

Operation

Hardware Data Protection

The command sequence requirement of unlock cycles

for programming or erasing provides data protection

against inadvertent writes (refer to the Command Defi-

nitions table). In addition, the following hardware data

protection measures prevent accidental erasure or pro-

gramming, which might otherwise be caused by spuri-

ous 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.

START

Perform Erase or

Program Operations

RESET# = VIH

Temporary Sector Group

Unprotect

Completed (Note 2)

RESET# = VID

(Note 1)

Notes:

1. All protected sector groups unprotected.

2. All previously protected sector groups are protected

once again.

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