Since ARM does not have a BIOS, how can ARM be password protected like a BIOS can be password protected? Thank you.
You just write suitable code. But then you first have to decide what hardware interface a user is expected to make use of to enter the password so your program will know if it should stay in locked mode or start doing whatever your device is intended to do.
Another thing - exactly what does "serial number" have to do with passwords?
What does ARM have to do with C51?