1. A data transmission circuit, comprising: a first bus segment of a data bus; a second bus segment of said data bus; and a first switching circuit connected between said first and second segments of said data bus, wherein said first switching circuit is configured to selectively connect said first and second segments of said data bus such that when said first switching circuit is in a first state, said first switching circuit passes data through from said first bus segment to said second bus segment and from said second bus segment to said first bus segment, and when said first switching circuit is in a second state, said second bus segment is disconnected from said first bus segment and data is passed through from said first bus segment to at least one I/O circuit and from said at least one I/O circuit to said first bus segment.