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AM29F400BT-90DPI1

4 Megabit (512 K x 8-Bit/256 K x 16-Bit) CMOS 5.0 Volt-only Boot Sector Flash Memory

Advanced Micro Devices 

PRELIMINARY

Table 4. Am29F400B Autoselect Codes (High Voltage Method)

Description

A17 A11

A8

A5

DQ8

to to

to

to

to

Mode CE# OE# WE# A12 A10 A9 A7 A6 A2 A1 A0 DQ15

DQ7

to

DQ0

Manufacturer ID: AMD

L

L

H X X VID X L X L L

X

01h

Device ID:

Word L

L

H

22h

23h

Am29F400B

X X VID X L X L H

(Top Boot Block)

Byte L

LH

X

23h

Device ID:

Word L

L

H

22h

ABh

Am29F400B

X X VID X L X L H

(Bottom Boot Block) Byte L

L

H

X

ABh

Sector Protection Verification L

L

H SA X VID X L X H L

X

01h

(protected)

X

00h

(unprotected)

L = Logic Low = VIL, H = Logic High = VIH, SA = Sector Address, X = Don’t care.

Sector Protection/Unprotection

The hardware sector protection feature disables both pro-

gram and erase operations in any sector. The hardware

sector unprotection feature re-enables both program and

erase operations in previously protected sectors.

Sector protection/unprotection must be implemented

using programming equipment. The procedure re-

quires a high voltage (VID) on address pin A9 and OE#.

Details on this method are provided in a supplement,

publication number 20185. Contact an AMD represent-

ative to obtain a copy of this 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

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 1 shows the algorithm, and

Figure 18 shows the timing diagrams, for this feature.

START

RESET# = VID

(Note 1)

Perform Erase or

Program Operations

RESET# = VIH

Temporary Sector

Unprotect Completed

(Note 2)

Notes:

21505C-5

1. All protected sectors unprotected.

2. All previously protected sectors are protected once

again.

Figure 1. 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

10

Am29F400B

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