MBM29DL640E Fujitsu Microelectronics, Inc., MBM29DL640E Datasheet - Page 32

• Manufacturer Part Number: MBM29DL640E
• Description: Flash Memory 64 M 8 M X 8/4 M X 16 Bit Dual Operation
• Manufacturer: Fujitsu Microelectronics, Inc.

32
MBM29DL640E
Hidden ROM (Hi-ROM) Region
Hidden ROM (Hi-ROM) Entry Command
Hidden ROM (Hi-ROM) Program Command
Hidden ROM (Hi-ROM) Protect Command
The Hi-ROM feature provides a Flash memory region that the system may access through a new command
sequence. This is primarily intended for customers who wish to use an Electronic Serial Number (ESN) in the
device with the ESN protected against modification. Once the Hi-ROM region is protected, any further modifi-
cation of that region becomes impossible. This ensures the security of the ESN once the product is shipped to
the field.
The Hi-ROM region is 256 bytes in length and is stored at the same address of the “outermost” 8 Kbyte boot
sector in Bank A. The device occupies the address of the byte mode 000000h to 0000FFh (word mode 000000h
to 00007Fh) . After the system has written the Enter Hi-ROM command sequence, the system may read the Hi-
ROM region by using the addresses normally occupied by the boot sector (particular area of SA0) . That is, the
device sends all commands that would normally be sent to the boot sector (particular area of SA0) to the Hi-
ROM region. This mode of operation continues until the system issues the Exit Hi-ROM command sequence,
or until power is removed from the device. On power-up, or following a hardware reset, the device reverts to
sending commands to the boot sector.
When reading the Hi-ROM region, either change addresses or change CE pin from “H” to “L”. The same procedure
should be taken (changing addresses or CE pin from “H” to “L”) after the system issues the Exit Hi-ROM command
sequence to read actual memory cell data.
The device has a Hidden ROM area with One Time Protect function. This area is to enter the security code and
to unable the change of the code once set. Programming is allowed in this area until it is protected. However,
once it gets protected, it is impossible to unprotect. Therefore, extreme caution is required.
The hidden ROM area is 256 bytes. This area is normally the “outermost” 8 Kbyte boot block area in Bank A.
Therefore, write the Hidden ROM entry command sequence to enter the Hidden ROM area. It is called Hidden
ROM mode when the Hidden ROM area appears.
Sectors other than the boot block area SA0 can be read during Hidden ROM mode. Read/program of the Hidden
ROM area is possible during Hidden ROM mode. Write the Hidden ROM reset command sequence to exit the
Hidden ROM mode. The bank address of the Hidden ROM should be set on the third cycle of this reset command
sequence.
In Hidden ROM mode, the simultaneous operation cannot be executed multi-function mode between the Hidden
ROM area and the Bank A.
To program the data to the Hidden ROM area, write the Hidden ROM program command sequence during Hidden
ROM mode. This command is the same as the usual program command, except that it needs to write the
command during Hidden ROM mode. Therefore the detection of completion method is the same as in the past,
using the DQ
programmed. If an address not in the Hidden ROM area is selected, the previous data will be deleted.
There are two methods to protect the Hidden ROM area. One is to write the sector group protect setup command
(60h) , set the sector address in the Hidden ROM area and (A
sector group protect command (60h) during the Hidden ROM mode. The same command sequence may be
used because it is the same as the extension sector group protect in the past, except that it is in the Hidden
ROM mode and does not apply high voltage to the RESET pin. Please refer to “Function Explanation Extended
Sector Group Protection” for details of extension sector group protect setting.
The other method is to apply high voltage (V
and (A
protect circuit, apply high voltage (V
in the Hidden ROM area, and read. When “1” appears on DQ
on DQ
0
6
, A
if it is not protected. Apply write pulse again. The same command sequence could be used for the above
3
, A
2
7
, A
data pooling, DQ
1
, A
0
)
(0, 0, 0, 1, 0) , and apply the write pulse during the Hidden ROM mode. To verify the
80/90/12
6
toggle bit and RY/BY pin. You should pay attention to the address to be
ID
) to A
9
, specify (A
ID
) to A
9
and OE, set the sector address in the Hidden ROM area
6
, A
3
, A
0
2
, the protect setting is completed. “0” will appear
6
, A
, A
1
, A
3
, A
0
)
2
, A
1
(0, 0, 0, 1, 0) and the sector address
, A
0
)
(0, 0, 0, 1, 0) , and write the