BUS MASTERING

5/25/96

Bus Mastering: A bus is a set of wires with associated electronic signals. To avoid contention between devices, most buses have a controller that sequences activities on the bus much as a traffic policeman controls traffic flow at a busy intersection. Bus control requires an exchange of signals requesting and obtaining permission to post/accept data. The speed of data transfers may be limited by the protocol required for bus access. In that case there can be a provision to shut down the normal controller and to give up bus control to a device that needs to do high speed data transfers. That device must negotiate control with the normal controller and must provide all the signals necessary to transfer data and to satisfy other devices on the bus during the time it is controlling the bus. Such a device is known as a bus mastering device or controller. It is possible to have several different bus mastering devices in a system designed to handle multiple bus masters, but only one can actually control the bus at any given time.