Firmware for PLC System 300S (317-4PN23) Firmware files have the following name structure: Name_ax_Vyyy.zip Name = name/order number of module, e.g. CPU 315-2AG13 ax = hardware version, e.g. a1 for release 1, a2 for release 2 Vyyy ... = firmware version e.g. V3061500 for version 3.6.15