MPC5775K's secure problem

[xiaoliu]

Hello,experts,

Recently,I am using the MPC5775K now .To prevent unauthorized people operating flash ,I want to change the password.From the manual 《MPC5775KRM_Rev3.4》,I think to add DCF record can make it.

Relevant instructions are NVSCI record、NVPWDH DCF record and NVPWDL DCF record.

From the manual ,if configure Censorship Control 0x55AA，the microcontroller will go to censor mode,!55AA will go to uncensor mode.If the microcontroller went to censor mode,it need input private password to operate the microcontroller.

So I did some test use 3 microcontroller.

Step 1:microcontroller 1,write NVPWDH DCF record and NVPWDL DCF record in Utest Flash to update password,then I found I Couldn’t connect the Emulator,neither the old password nor the new password ;

Step2: microcontroller 2,write NVSCI record、 NVPWDH DCF record and NVPWDL DCF record in Utest Flash to update password, configure Censorship Control !0x55AA，the microcontroller will go to uncensored mode,I found no password could connect the Emulator now,but I changed to censor mode,it didn’t work,the microcontroller still need no password.

Step3: microcontroller 3,write NVSCI record、 NVPWDH DCF record and NVPWDL DCF record in Utest Flash to update password, configure Censorship Control 0x55AA，the microcontroller will go to censored mode,I found only new password could connect the Emulator.And I changed the password again, the microcontroller couldn’t connect the Emulator in any password.

So I have 3 questions,

Q1:should NVSCI record、 NVPWDH DCF record and NVPWDL DCF record write at the same time to change the password?Can I do thing to microcontroller1 and 3 now?

Q2: From the step 2,is microcontroller’s censored or uncensored mode can be set only once?

Q3: From the step4,is microcontroller’s private password can be set only once?

Best regards!!!!!

[petervlna]

Hi,

The password DCF record must be updated (NVPWDL and NVPWDH) before reset occurs.

To modify an already programmed password new records may be simply appended to overwrite the previous password

Peter

[petervlna · Accepted solution]

Hello,

A1:NVPWDH DCF record and NVPWDL DCF record must be present in DCF utest area in same time. I am not sure what you mean by "same time".

A2: Yes, NVSCI record must be updated only once using the DCF records.

A3:To modify an already programmed password new records may be simply appended to overwrite the previous password.

[xiaoliu]

Hi,Peter VIna,Can you help me to answer my new questions?

[xiaoliu]

Thank you for your reply! I understand some reason of my test,and I still have some confused part.

Q1:The "Same time" mean : Last time I powered on the microcontroller,I only wrote NVPWDL DCF record,then I powered off the microcontroller.  After these operations, any password is not OK now. I think these operations my be wrong,Do I have any remedy operation?

Q2:In my test step 3,I updated the password the 2nd time,my operations were writing NVSCI record 、 NVPWDH DCF record and NVPWDL DCF record again. It means I wrote the NVSCI record twice. I think it's the reason why I can't  connect the Emulator in any password. what do you think of my  deduction?