MC68HC908GR60A security field values restriction?

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MC68HC908GR60A security field values restriction?

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guide19
Contributor II

Hi,

I am trying to program the address 0xFFF6-FFFD with values 0x00. But after programming and verifying the flash memory the MCU seems to be secured.
Read values are 0xAF. Is it possible to program all security bytes with 0x00?
Is there any restriction which value should or should not be at 0xFFF6-FFFD?
When I program random data at 0xFFF6-FFFD then the verify is OK.

BR,
Jozef

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Rick_Li
NXP Employee
NXP Employee

Hi Jozef,

No matter what value programmed in memory address 0xFFF6-0xFFFD, the flash will be security after programmed.

For security reason, please do not leave 0xFFF6~0xFFFD to blank.

And there is no restriction on the value be programmed at 0xFFF6~0xFFFD, but you need to know the data that has been programmed for monitor mode entry.

Please see section '19.3.2 Security' of MC68HC908GR16 for further reference!

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guide19
Contributor II

Hi Yong Li,

>No matter what value programmed in memory address 0xFFF6-0xFFFD, the flash will be security after programmed.

Yes I have the same experience, but for that case it seems that something is not working OK.

I also realized, that when I program security values on 0XFFF6-0xFFFD where minimum 5 from 8 bytes are equal 0x00 (doesn't matter what position they are) than even if I send correct security values at the beginning of entering Monitor mode, I am not able to read the MCU and it looks like the MCU is secured.

When maximum 4 from 8 security bytes are 0x00 than everything works how it should be.

Do you have this MCU in your office? is it possible to try program all security fields to 0x00 and test if everything works fine and you can re-read the device?

BR,

Jozef

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