This application note discusses the MAX3421E-Revisions 1 and 2 acting as a host USB controller. The MAX3421E sends data to a USB peripheral using a double-buffered Send FIFO. In Revs 1 and 2 of the part, special consideration is required for programming OUT transfers. This application note describes the sending mechanism. Example code for programming single-buffered and double-buffered OUT transfers is given.