Книга: Introduction to Microprocessors and Microcontrollers

Buses

These conductors are in groups, since many will be going to the same place for much the same purpose. For example, an 8-bit microprocessor normally uses 8 connectors to carry the data between the microprocessor and the memory. It would make diagrams very complicated if each wire were to be shown separately so we group them together and refer to them as the data bus. A bus is therefore a collection of conductors providing a similar function.

In a microprocessor-based system we have three main buses: the data bus, the address bus and a control bus. The data bus is a two-way bus carrying data around the system. Information going into the microprocessor and results coming out. The address bus carries addresses and is a one-way bus from the microprocessor to the memory or other devices. The control bus is rather different from the other two. It is a somewhat looser collection of conductors. If we look at a microprocessor-based system we can easily see the data and address buses since they consist of many parallel connections. However, the control bus is just an association of all the other necessary connections such as those to the chip select and read/write pins.

Address information, data and control signals have to be carried around inside the microprocessor as well as in the external system. We will therefore meet internal as well as external buses.

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