Abstract: An electrically programmable and erasable ROM (EPROM) is accessed via a selector and an address counter, all mounted on a PC board which includes also a regular VCC bus. The EPROM output lines feed an output circuit, parts of which may be on other boards. The board, however, has additional terminals connected to the EPROM output lines in addition to a protective circuit limiting the voltage level in the output circuit in case high reprogramming signals are applied by an external unit to some of these additional terminals for programming via the EPROM output terminal. One of the latter terminals connects to the VCC input of the EPROM and a Schottky diode connects the VCC bus to that input to protect the latter bus from a higher-than-normal supply voltage needed during reprogramming.