ADE7569 datasheet(98/136 Pages) AD

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ADE7566/ADE7569

Preliminary Technical Data

Rev. PrA | Page 98 of 136

PROTECTING THE FLASH

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 a unexpected disruption of the

normal execution of the program.

Write/erase protection is individually selectable for all of the

32 pages. Read protection is selected in groups of 4 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); 4 bytes are reserved for

write/erase protection, 1 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 to be 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

using 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.

PROTR

PROTKY

PROTB0

PROTB1

EADRL

EADRH

31–28

27–24

23–20

19–16

15–12

11–8

7–4

3–0

PROTECTION KEY

0x3FFF

0x3FFE

0x3FFD

0x3FFC

0x3FFB

0x3FFA

0x3FF9

0x3E00

WDOG

LOCK

Figure 81. Flash Protection in Page 31

The sequence for writing the protection bits is as follows:

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

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 0x0 to the ECON

Reset the chip to activate the new protection.

To enable read and write/erase protection for the last page only,

use the following 8051 code. Writing the flash protection

command to the ECON register initiates programming the

protection bits in the flash.

; enable write/erase protection on the last page only

MOV EADRH, #07FH

MOV EADRL, #0FFH

MOV PROTB1, #FFH

MOV PROTB0, #FFH

; enable read protection on the last four pages only

MOV PROTR, #07FH

; set up a protection key of 0A3H. This command can be

; omitted to use the default protection key of 0xFF

MOV PROTKY, #0A3H

; write the flash key to the FLSHKY register to enable flash

; access. The flash access key is not configurable.

MOV FLSHKY, #3BH

; write flash protection command to the ECON register

MOV ECON, #08H

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