AM29F400B AMD [Advanced Micro Devices], AM29F400B Datasheet - Page 10

• Manufacturer Part Number: AM29F400B
• Description: 4 Megabit (512 K x 8-Bit/256 K x 16-Bit) CMOS 5.0 Volt-only Boot Sector Flash Memory
• Manufacturer: AMD [Advanced Micro Devices]

L = Logic Low = V
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 (V
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 V
sectors can be programmed or erased by selecting the
sector addresses. Once V
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.
10
Manufacturer ID: AMD
Device ID:
Am29F400B
(Top Boot Block)
Device ID:
Am29F400B
(Bottom Boot Block)
Sector Protection Verification
Description
ID
. During this mode, formerly protected
IL
, H = Logic High = V
Mode
Word
Word
Byte
Byte
Table 4. Am29F400B Autoselect Codes (High Voltage Method)
ID
) on address pin A9 and OE#.
ID
CE#
is removed from the RE-
L
L
L
L
L
L
OE#
IH
L
L
L
L
L
L
, SA = Sector Address, X = Don’t care.
WE#
H
H
H
H
H
H
P R E L I M I N A R Y
A17
A12
SA
to
X
X
X
Am29F400B
A11
A10
to
X
X
X
X
V
V
V
V
A9
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
Notes:
1. All protected sectors unprotected.
2. All previously protected sectors are protected once
Figure 1. Temporary Sector Unprotect Operation
ID
ID
ID
ID
again.
A8
A7
to
X
X
X
X
A6
L
L
L
L
A5
A2
to
X
X
X
X
Unprotect Completed
Program Operations
Temporary Sector
Perform Erase or
A1
H
L
L
L
RESET# = V
RESET# = V
(Note 1)
(Note 2)
START
A0
H
H
L
L
DQ15
DQ8
22h
22h
ID
IH
to
X
X
X
X
X
(unprotected)
(protected)
DQ7
DQ0
ABh
ABh
01h
23h
23h
01h
00h
21505C-5
to