Data transmission apparatus, system and method, and image processing apparatus

摘要

A host computer logs in an image providing device such as a scanner connected by a serial bus, and reverses flow control of data transfer by issuing a Reverse command. The image providing device opens a transfer channel by an OpenChannel command, transfers image data in form of blocks. When the transfer of the image data has been completed, the image providing device closes the transfer channel by a CloseChannel command, and reverses the flow control of the data transfer again by the Reverse command. This changes the data transfer direction of a device having a bidirectional data transfer function, i.e., a device having a data reception function and a data providing function.