Abstract: A plurality of state machines arranged into three functional units, an Upper Machine, Middle Machine and a Lower Machine facilitate movement of user data between a buffer memory and a Global Memory (GM) in a data transfer interface. The Middle Machine controls all data movement to and from the GM. Although not directly in the data path, it is responsible for coordinating control between elements that comprise data transfer channels. The Middle Machine is interconnected to and provides control and coordination between the Upper and Lower sides of the buffer memory. The Lower Machine connects to a data assembly mechanism of each pipe. The Upper Machine connects to the backplane, which in turn connects to Global Memory. The actual data transfers between the buffer memory and GM are controlled by the Upper Machine, and transfers between the buffer memory and the data assembly mechanism are controlled by the Lower Machine.