Welcome to the 4th lecture or that is the 4th unit of the module on addressing mode, instruction set and instruction execution flow. (Refer Slide Time: 00:35) So, in the last three units we have basically discussed what is a CPU? What it consists of; and how it is interfaced with the main memory and then we have gone into the details of basically, what is the basic motive of this module is to understand how a basically an instruction executes in a CPU. So, in that in that direction, first we had seen in the last unit that how our instruction is basically executed.

So, now in today’s unit we are going to focus on instruction format, because as I told you this module will mainly deliver or you will be able to understand, basically how to design an instruction given a set of requirements or a set of specification that is the main goal actually. So, for that we first now look in a more generic fashion that what is an instruction and what is the basic format?

the in this unit basically you will be studying the generic format of an instruction. So, as an instruction as we have discussed in the last unit that basically an instruction executes or does the general operations in a computer. So, if there is an operation to be done. So, we require basically two things one is, what operation I have to do? And, basically on what operands you have to do the operation. So, basically opcode and source and result operands these are the two very important things.

So, if I order you something. So, I have to tell you, what to do and also I have to tell you on what objects you have to do the operation and where you have to store the result. So, that is actually called the opcode; that is, what operation you have to do?

Like for example, you have to move an operand, you have to add two numbers etcetera, etcetera. And then you have to tell that what are the operands? That is the in case of a computer the operands are actually some immediate operations some immediate values which are specified in the instruction or in the more broad terms for the time being you can think that the values of the operands, that is the variables and the values of the variables are stored in some memory if it’s a Von Neumann architecture.

But, when you are thinking over computer perspective or a code perspective, then after one instruction you have to execute another instruction. So, of course, you have to also tell in that instruction that which is the next instruction to be fetched.

So, there are basically that therefore actually the next part means of basically; if these things are more or less of basic prerogative of an instruction that these are the basic stuff required like opcode, source, destination and what next instruction and basically three categories of instruction like arithmetic, logic etcetera.

So, if you take a logical memory operation. So, sorry in arithmetic operation, we generally have two operands it can be add, multiply, subtract. And generally we take two sometimes unary operations unary operands also can be there like for example, this is the number you want to negate it.

Before you go to the main stuff. Actually, as I told you that all these instructions basically are represented in binary like for add there should be an opcode and there may be the representation of can be 101.

So, therefore, with all these mnemonics, these are actually these abbreviations are called basically mnemonic way of representation like instead of add instead of 101, we will write add sub we will not write the binary version.

So, what are the objectives? That is going to we are going to fulfil after doing this unit basically we will be available to describe you will develop knowledge...

So, now we have told so many theories. So, let us try to give some proper examples. So, it’s an example of an instruction of a three instruction; three address instruction add 𝑅1 3030 hex and 3031 hex.