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ADE7518
PROTECTING THE FLASH MEMORY
The sequence for writing the protection bits is as follows:
Two forms of protection are offered for this flash memory: read
protection and write/erase protection. The read protection ensures
that any pages that are read protected are not able to be read by
the end user. The write protection ensures that the flash memory
cannot be erased or written over. This protects the end system
from tampering and can prevent the code from being overwritten
in the event of an unexpected disruption of the normal execution
of the program.
Write/erase protection is individually selectable for all 32 pages.
Read protection is selected in groups of four pages (see Figure 79
for the groupings). The protection bits are stored in the last flash
memory locations, Address 0x3FFA through Address 0x3FFF (see
Figure 81); four bytes are reserved for write/erase protection,
one byte is for read protection, and another byte sets the protection
security key. The user must enable read and write/erase protection
for the last page for the entire protection scheme to work.
Note that the read protection does not prevent MOVC
commands from being executed within the code.
There is an additional layer of protection offered by a protection
security key. The user can set up this security key so that the
protection scheme cannot be changed without this key. Once
the protection key has been configured, it cannot be modified.
Enabling Flash Protection by Code
The protection bytes in the flash memory can be programmed
1.
2.
3.
4.
5.
Set up the EADRH, EADRL, PROTB1, and PROTB0
registers with the write/erase protection bits. When erased,
the protection bits default to 1 (like any other bit of flash
memory). The default protection setting is for no protection.
To enable protection, write a 0 to the bits corresponding to
the pages that should be protected.
Set up the PROTR register with the read protection bits.
Note that every read protection bit protects four pages.
To enable the read protection bit, write a 0 to the bits that
should be read protected.
To enable the protection key, write to the PROTKY register.
If enabled, the protection key is required to modify the
protection scheme. The protection key, Flash Memory
Address 0x3FFA, defaults to 0xFF; if the PROTKY register
is not written to, it remains 0xFF. If the protection key is
written to, the PROTKY register must be written with this
value every time the protection functionality is accessed.
Note that once the protection key is configured, it cannot
be modified. Also, note that the most significant bit of
Address 0x3FFA is used to enable a lock mechanism for
the watchdog settings (see the Watchdog Timer section
for more information).
Run the protection command by writing 0x08 to the
ECON register.
Reset the chip to activate the new protection.
using the flash controller command and programming ECON to
0x08. In this case, the EADRH, EADRL, PROTB1, and PROTB0
bytes are used to store the data to be written to the 32 bits of write
protection. Note that the EADRH and EADRL registers are not
used as data pointers here but to store write protection data.
To enable read and write/erase protection for the last page only, use
the following 8052 code. Writing the flash protection command
to the ECON register initiates programming of the protection
bits in the flash.
; enable read protection on the last four
EADRH
EADRL
0x3FFF
0x3FFE
WP
31
WP
23
WP
30
WP
22
WP
29
WP
21
WP
28
WP
20
WP
27
WP
19
WP
26
WP
18
WP
25
WP
17
WP
24
WP
16
pages only
MOV PROTR,#07Fh
PROTB1
PROTB0
0x3FFD
WP
15
WP
WP
14
WP
WP
13
WP
WP
12
WP
WP
11
WP
WP
10
WP
WP
9
WP
WP
8
WP
; set up a protection key of 0A3h. This
command can be
PROTR
0x3FFC
7
RP
6
RP
5
RP
4
RP
3
RP
2
RP
1
RP
0
RP
; omitted to use the default protection key
of 0xFF
PROTECTION KEY
0x3FFA
PROTKY
0x3FFB 31:28 27:24 23:20 19:16 15:12 11:8 7:4
WDOG
LOCK
0x3FF9
3:0
MOV PROTKY,#0A3h
; write the flash key to the FLSHKY register
to enable flash
; access. The flash access key is not
configurable.
0x3E00
Figure 81. Flash Protection in Page 31
MOV FLSHKY,#3Bh
; write flash protection command to the ECON
register
MOV ECON,#08h
Rev. 0 | Page 91 of 128
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