The MFR_SPECIFIC_42 command can be optionally used to set a password for NVM programming. To prevent a hacker from simply sending the password command with all possible passwords, the TPSM831D31 goes into a special extra-secure state when an incorrect password is received. In this state, all passwords are rejected, even the valid one. The device must be power cycled to clear this state so that another password attempt may be made. When NVM security is enabled, the TPSM831D31 will not accept writes to any command other than PAGE and PHASE, which are necessary for reading certain parameters.

Enabling NVM Security

1. Set the NVM password. Write MFR_SPECIFIC_42 to a value other than FFFFh.
2. Issue STORE_DEFAULT_ALL
3. Wait 100ms for the NVM store to complete
4. Power cycle V3P3. NVM Security will be enabled at the next power-up.

Disabling NVM Security

To disable NVM security, use the following procedure:

1. Write the password to MFR_SPECIFIC_42 to disable NVM security. Once the correct password has been given, NVM security will be disabled, and the device will once again accept write transactions to configuration registers.

NVM security will be re-enabled at the next power-on, unless MFR_SPECIFIC_42 is set to FFFFh (NVM Security Disabled), and an NVM store operation (issue STORE_DEFAULT_ALL and wait 100 ms) is performed.

Determining Whether NVM Security is Active

Reads to the MFR_SPECIFIC_42 command returns one of three values:

• 0000h = NVM Security is Disabled
• 0001h = NVM Security is Enabled
• 0002h = MFR_SPECIFIC_42 is locked due to incorrect password entry