In any microprocessor system, the system bus consists of a number of separate lines. Each line is assigned a particular function. Fundamentally in any system, the system bus can be classified into three functional groups: the address, the data and control lines or buses.
The data bus provides path for transferring data between the microprocessor system and the peripherals.
The data bus consists of a number of separate lines, generally 8, 16, 32 or 64. The number of lines is referred as the width of the data bus.
Since, each line carry only one bit at a time, the number of lines determines how many bits can be transmitted at a time.
The width of data bus is a key factor in determining the overall system performance.
The address bus which consists of a number of separate lines, are used to designate the source or destination of the data on data bus. For example, if the CPU requires reading a word (8, 16, 32 or 64 bits of data) from memory, it put the address of the desired word on the address bus.
The width of address bus (i.e number of lines) determines the maximum possible memory capacity of the system.
The address bus is also used to address IO ports.
The control bus is a group of lines used to control the access to and the use of the data and address bus since the data and address bus are shared by all components of microcomputer system. Hence control bus provides a means of controlling their use.
The control bus carries the control signals. The control signals transmit both command and timing information between the system modules.
The timing signals indicate the validity of data and address information; whereas the command signals specify the operations to be performed.
Some control signals are: Memory Read, Memory Write, IO Read, IO Write, Interrupt Request, Interrupt Acknowledge, Bus request, Bus Grant etc
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