Exiting Serial Programming Mode
To exit the serial programming mode, you should send the Logout (O) command . It is important to send this command, and not the Reboot (E) command . When rebooting the device, all current parameters (modem commands) are lost. Thus, the parameters you've entered in the programming session just ended will be lost and will have no effect on the DS.
This is why it's important to remember -- To exit Serial Programming Mode, use the Logout (O) command .