Always programmers lock the programmed CPU by a password to protect their software. As always we say, the software is the programmer know-how, so it's for him. The client own the CPU as a hardware and also the application. i.e. he could use the software for his application but he is not authorized to modify, delete or add any thing to the software without notifing the programmer.
So, Siemens make passwords of the CPUs (in case of selecting this option) to protect the programs from un-authorized access. To access the software, you must ask the programmer for the password!
As I told before that the client own both the application and also the H/W. So, there is a master password you can use to erase and only erase the software from the CPU and then, the CPU will be returned into factory setting. i.e. a blank CPU. You can pragram it as you like. Without this password. So, it will not help you to upload the software!
The master erasing password: CLEARPLC
1. Choose PLC> clear menu command to display the "Clear" dialog box.
2. Select all the check boxes and click "OK"button to verify the measures taken.
3. If the password has been configured, STEP 7-Micro/WIN a password authentication dialog box is displayed. To clear the password, the password authentication dialog box, enter CLEARPLC, continue to implement the "All Clear"operation. (CLEARPLC password is not case-sensitive.)