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Common Bus System using multiplexers

  • Difficulty Level : Hard
  • Last Updated : 20 May, 2020

A typical computer has many registers and we need to transfer the information between these registers. A way to transfer the information is using the common bus system. In this article we shall discuss the common bus system using multiplexers.

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Let’s discuss the common bus system with multiplexers.



The construction of this bus system for 4 registers is shown above. The bus consists of 4×1 multiplexers with 4 inputs and 1 output and 4 registers with bits numbered 0 to 3. There are 2 select inputs S0 and S1 which are connected to the select inputs of the multiplexers.

The output 1 of register A is connected to input 0 of MUX 1 and similarly other connections are made as shown in the diagram. The data transferred to the bus depends upon the select lines. A table for the various combinations of select lines is shown below.

Select Lines combination S1S0Register Selected
00Register A
01Register B
10Register C
11Register D

As we can see that when S1S0=00, register A is selected because on 00 the 0 data inputs of all the multiplexers are applied to the common bus.

Since the 0 data inputs of all the multiplexers receive the inputs from the register A, thus register A gets selected. Similarly for other combinations of S1S0 other register are selected.

Note-

No. of multiplexers needed = No. of bits in each register 
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