Option-identifying system

An option-identifying system identifies the locations of a plurality of options that are electrically connected in cascade and mounted to a main body such that the options are attachable to and detachable from the main body. The main body outputs a location-assigning signal having a plurality of bits to a first one of the plurality of options. Each option tray has a data-storing section and a location-identifying section. The data-storing section stores the locations of the plurality of options and corresponding location data that describes the locations. The location-identifying section receives the location-assigning signal and compares the received location-assigning signal with the location data to identify a location of a corresponding option. The location-identifying section changes the logic level of at least one bit of the received location-assigning signal or changes the number of bits of the received location-assigning signal, then outputs to a immediately lower option tray.