Understanding Computer Architecture: System Bus, Address Bus, Data Bus, and Control Bus

System Bus (Data, Address, and Control Bus)

This network of wires or electronic pathways is called the 'Bus'. A system bus is a single computer bus that connects the major components of a computer system.

It combines the functions of:

• Data Bus: Carries information.
• Address Bus: Determines where information should be sent.
• Control Bus: Determines the operation to be performed.

This technique was developed to reduce costs and improve modularity.

Figure: System Bus

Address Bus

The address bus is a group of wires or lines used to transfer the addresses of memory or I/O devices.

• It is unidirectional.
• The width of the address bus determines the maximum addressing capacity, representing the largest address within memory that the bus can handle.
• Addresses are transferred in binary format, with each line carrying a single binary digit (bit).
• Therefore, the maximum address capacity is equal to 2 raised to the power of the number of lines present (2^lines).

Data Bus

The data bus transfers data between the microprocessor and memory or input/output devices.

• It is bidirectional, allowing the microprocessor to both send and receive data.
• Each wire carries signals corresponding to a single bit of binary data.
• A wider data bus enables the transfer of larger amounts of data simultaneously.

Control Bus

The microprocessor uses the control bus to manage data operations, dictating how to interact with the selected memory location.

• Examples of control signals include Read, Write, and Opcode fetch.
• The control bus facilitates various microprocessor operations.
• It is a dedicated bus, with all timing signals generated based on the control signal.

Microprocessor Systems with Bus Organization

Figure: Microprocessor Systems with Bus Organization

To perform meaningful tasks, a microprocessor requires support from other auxiliary devices. In its simplest form, a microprocessor-based system comprises a microprocessor, I/O (input/output) devices, and memory. These components are interconnected through a shared communication pathway known as the system bus.

Here's a breakdown of the typical structure:

• Microprocessor: Acts as the master, executing programs and coordinating with connected peripherals.
• Memory: Stores both programs and data. Systems typically include ROM (Read Only Memory, non-volatile) and RAM (Random Access Memory, volatile).
• I/O Devices: Enable communication with the external environment. Examples include keyboards (input) and LEDs, LCDs, or monitors (output).

The complexity of microprocessor-based systems varies depending on the application, ranging from simple devices like washing machines to sophisticated computers.