I have a PV 300 Keypad, no PLC, no cable for computer. I need to clear the memory in this unit. When I press the left and right arrow keys simultaneously, I get what looks like a lock or key on the screen. It is partially hidden by the banner that states "612 No Active Nodes". I tried a few combinations on the power up trick when the boot sequence gets to 32, but have not found the correct one. Does anyone know how I can clear the memory in the unit? Unit is a 2711-K3AL21.