How to Control Common Bus in Computer Architecture?

Computer Architecture Computer Science Network

A bus is a structure that handles the data transmission in a computer system or network. The common bus of 16-bit is controlled by the selection inputs S₂, S₁ , and, S₀.

Each binary number is associated with a Boolean variable x₁ through x₇, corresponding to the gate structure that must be active to select the register or memory for the bus.

For example, when x₁ = 1, the value of S₂, S₁ , and, S₀ must be 001 and the output of AR will be selected for the bus.

The decimal number shown with each bus input indicates the binary equivalent that must be applied to the selection inputs. This is helpful while selecting the appropriate register.

The table shows the register that is to be chosen for the particular binary numbers of selection inputs.

Inputs							Outputs			Register to be selected for bus
X1	X2	X3	X4	X5	X6	X7	S2	S1	S0
0	0	0	0	0	0	0	0	0	0	None
1	1	1	1	1	1	1	0	0	0	AR
0	0	0	0	0	0	0	0	1	0	PC
0	0	0	0	0	0	0	0	1	0	DR
0	0	0	0	0	0	0	1	0	1	AC
0	0	0	0	0	0	0	1	0	1	IR
0	0	0	0	0	1	0	1	1	0	TR
0	0	0	0	0	0	1	1	1	1	Memory

Each of the binary numbers is related with a Boolean variable x₁ through x₇ in the figure.

The encoder Boolean functions are as follows −

S₀ = x₁ + x₃ + x₅ + x₇

S₁ = x₂ + x₃ + x₆ + x₇

S₁ = x₄ + x₅ + x₆ + x₇

The logic for each encoder input can be determined if control functions that place the corresponding register onto the bus, are found.

Ginni

Updated on: 24-Jul-2021

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