Hi tomexx,
Usually all programmer must blank with FFs. case not... will not be considered as blank. FF is a safe way to test blank.

BUT be sure your programmer erase EEPROM memory when programming.

To test a password... you can have a maximum lenght of character. when you write it to eeprom use always a fix sized. others unused character in password can be filled with 0s or FF or if you want an special character to gives you the end point of your password. This allows to test password lenght while entering.

regards