We know that our control unit perform two basics function

We have already studied data control. In this lecture we will try to understand , what is data path control.

Q. What is Data Path control with respect to architecture and organization

Ans: it means that how we can put various components togather so whenever the processor needs, the control unit can issue control signals, so that physical connection can be enabled, so data can move around.

In above discussion we have three main components

1. Components

2. Control Signals

3. Data Path

We will here now try to understand them one by one

The Components

Some of the general components are

1.MUX

2.ALU

3.Registers

MUX

By mux we mean multiplexer .A multiplexer (or mux) is a device that selects one of the many input signals and forwards the selected input to out put.

The mux chooses the input by sletion line. It means that we can have any input as output , depending on section line

In above digram , M is out put and A B C D are input . Now depending on selection lines s1 and s2 , the mux will choose only one input and will route it to out put.

e.g. If S1 and S2=00 than M= 0

.

Arithmetic Logic Unit

An AlU is a device that carries out mathematical and logical functions. Mathmatical functions include “+”, “ – “ and logical functions include function like “=” “>”

ical functions include function like “=” “>”

One of the very interesting function of ALU is that it can chooses one input from many inputs, and can send it to out put without performing any functions . Example output=Input or A= B

The Symbol of ALU Is

The above ALU have 5 conroller lines, it means that we can have 25=32 individual unique codes. Every code can be given a specific operation like + – > =.

Hene a ALU with 32 bits can have 32 operations, out of which few can be of mathematical and other can be of logical .

Size of ALU

The Size of ALU is defined as , the number of bits it can process at a time. A typical ALU can be of 4 bits 8 bit 16 bit etc.

Registers.

Registers are electronic manuals that can store data temporary. Some of the registers are as follow.

1. Address Register.

Holds the address of the current instruction or data. The address register points towards the memory location

………………………………

Program Counter

Another register with name of program counter tells addres register that where next address is. It’s a type of a counter which tell address register that how should it move to next memory cell like =current memory location +5

Data register

Data registers hold the data which is obtained from memory via data bus .

Instruction Register

Instruction register hold instruction

Data Path Exercise time

Let’s say we have two register, data register and program counter. And we want to select such a data path that only data from data register is obtained on out put

Question 2 : Make a digram that show how data path can be constructed , so that instruction from program counter can be send to Address register

Question 3: change the above diagram so that data from data register 1 and data register 2 can be sent to ALU for any function or process

Question 4: Show circuit digram , in which instruction from memory is sent to instruction register

Data Path Architecture