PC = 789 H
How CPU to fetch the instruction (binary code) from memory using common bus
Notably, with the provided data, we can fetch binary code instruction utilizing the common bus
First we must understand that a bus is a set of common wires that carries data between registers.
– There is a separate wire for every bit in the registers. – There are also a set of control signals
which determines which register is selected by the bus at a particular time.
A bus can be constructed using multiplexer which enable a sets of registers to share a common
bus for data transfer.
Specifically, for the PC of 789 H, we can select lines S1 and S0 indicate which of four register
will have its contents transferred to the bus.
A bus system will multiplex k registers of n bit each to produce a n–line common bus.
It will require n k x 1 multiplexers.
The bus is connected to the inputs of all destination registers, and will activate the load control of
the selected register when it is ready to transfer data. This can be written as: • R2 ← BUS, BUS