System bus

System Bus of a Processor

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• published: 14 Sep 2011
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System Bus of a ProcessorA system bus of a processor is used for data exchange between the processor and any devices within the microprocessor circuit (for instance, in controllers or computers).The devices that are always present in any microprocessor system include RAM, ROM, a timer, as well as input and output ports.Depending on the processor type a system bus may contain one or several address buses, one or several data buses, and a control bus. Only signalling processors use several data and address buses. They are necessary to increase the processor's capacity. General purpose processors and controllers usually have one address and one data bus.Bus as a notion can have different meanings depending on the topic. Usually a bus is a set of parallel wires transmitting binary code. Each wire carries a separate binary digit.Data can be transmitted in one direction, for instance, this is the case with address and control buses. It can also be transmitted in both directions, as in a data bus. A data bus carries data either to or from a processor depending on the operation performed by the latter. Data can be read or recorded.Sometimes a separate microcircuit (for instance, a DMA controller or a coprocessor) is used to control the system bus. This is done to increase the speed of data processing. In this case, the system bus controller also carries out the system bus access arbitration. (In the simplest case a busy signal is enough.)In some cases the notion also includes requirements related to voltage levels. The latter express the zeros and ones transmitted over the bus. The requirements may include the acceleration time of transmitted signals, the types of sockets and soldering-up, the sequence of transmitted signals, and the data transmission rate.