A medium support unit of a liquid ejection device has a negative pressure chamber and a medium support surface so that an ejection medium is supported on the medium support surface by suction, and includes a plurality of first recesses and at least one second recess. The system and method provide for decoding a first instruction into a plurality of operations with a decoder. The receptacle shield defines a receiving space for receiving the housing and exposing a plug receiving chamber of the housing to the outside, and includes two inward projecting prongs.