29F020 データシートの表示（PDF） - Advanced Micro Devices

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29F020

2 Megabit (256 K x 8-Bit) CMOS 5.0 Volt-only Boot Sector Flash Memory

Advanced Micro Devices 

Sector protection/unprotection must be implemented

using programming equipment. The procedure

requires a high voltage (VID) on address pin A9 and the

control pins. Details on this method are provided in the

supplements, publication numbers 20819

(Am29F002B) and 21183 (Am29F002NB). Contact an

AMD representative to obtain a copy of the appropriate

document.

The device is shipped with all sectors unprotected.

AMD offers the option of programming and protecting

sectors at its factory prior to shipping the device

through AMD’s ExpressFlash™ Service. Contact an

AMD representative for details.

It is possible to determine whether a sector is protected

or unprotected. See “Autoselect Mode” for details.

Temporary Sector Unprotect

Note: This feature requires the RESET# pin and is

therefore not available on the Am29F002NB.

This feature allows temporary unprotection of previ-

ously protected sectors to change data in-system. The

Sector Unprotect mode is activated by setting the

RESET# pin to VID. During this mode, formerly pro-

tected sectors can be programmed or erased by

selecting the sector addresses. Once VID is removed

from the RESET# pin, all the previously protected

sectors are protected again. Figure 1 shows the algo-

rithm, and the Temporary Sector Unprotect diagram

shows the timing waveforms, for this feature.

START

RESET# = VID

(Note 1)

Perform Erase or

Program Operations

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

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

accept 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.

RESET# = VIH

Temporary Sector

Unprotect

Completed (Note 2)

Notes:

1. All protected sectors unprotected.

2. All previously protected sectors are protected once

again.

Figure 1. Temporary Sector Unprotect Operation

November 28, 2000

Am29F002B/Am29F002NB

11

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