INTRODUCTION:

In computer central processing unit the micro-operations are detailed low-level instructions which is used in some designs to implement complex machine instructions.Usually, micro-operations perform basic operations on data stored in one or more register, including transferring data between registers or between registers and external buses of the CPU and performing arithmetic or logical operations on registers. The execution of micro-operations is performed under control of the CPU’s control unit which decides on their execution while performing various optimizations such as reordering, fusion and caching of the operations. micro operation have also been employed in a different way in order of modern MISC processors which is more easily handle asynchronous parallel execution.As with traditional microcode one or more table look ups is done to locate the appropriate micro operation-sequence based on the encoding and semantics of the machine instructions however, instead of having rigid micro operation-sequences controlling the CPU directly from a microcode-ROM, micro operations are dynamically buffered for rescheduling before being executed.

•The operations on the data in registers are called micro operations.

•The functions built into registers are examples of micro operations,

–Shift–Load –Clear –Increment etc ..

An elementary operation performed (during one clock pulse), on the information stored in one or more registers.
f: shift, load, clear, increment, add, subtract, complement, and, or, xor etc.Microoperations Set of allowable microoperations provided by the organization of the computer -Control signals that initiate the sequence of microoperations (to perform the specfic functions) . Screenshot (11).png

TYPES OF MICRO-OPERATION:

1:Register transfer micro-operations

2:Arithmetic micro-operations

3:Logic micro-operations

4: Shift micro operations

1:Register transfer micro-operations:

Register transfer language is a kind of intermediate representation (IR) that is very close to assembly language, such as that which is used in a compiler. It is used to describe data flow at the register transfer level of an architecture.A register transfer language is a system for expressing in symbolic form the micro operation sequences among the registers of a digital module. It is a convenient tool for describing the internal organization of digital computers in concise and precise manner. It can also be used to facilitate the design process of digital systems.These type of micro operations are used to transfer from one register to another binary information.

–>A symbolic language

–->A convenient tool for describing the internal organization of digital computers

–>Can also be used to facilitate the design process of digital systems

Registers are designated by capital letters, sometimes followed by numbers (e.g., A, IR)
Often the names indicate function:

–MAR – memory address register

–PC – program counter

–IR – instruction register

Registers and their contents can be viewed and represented in various ways

–A register can be viewed as a single entity,Registers may also be represented showing the bits of data they contain memory address.

Copying the contents of one register to another is a register transfer
A register transfer is indicated as

R2 ¬> R1

–In this case the contents of register R1 are copied (loaded) into register R2

–A simultaneous transfer of all bits from the source R1 to the destination register R2, during one clock pulse

–Note that this is a non-destructive; i.e. the contents of R1 are not altered by copying (loading) them to R2.

A register transfer such as

R3 ¬ R5

Implies that the digital system has the data lines from the source register (R5) to the destination register (R3) and Parallel load in the destination register (R3),it Control lines to perform the action.

HARDWARE IMPLEMENTATION:

2:Arithmetic micro-operations:

These micro-operations are used to perform on numeric data stored in the registers some arithmetic operations.A micro operation is an elementary operation performed on the information stored in one or more registers. The micro operation in digital computers are of 4 types:Addition,Subtraction,Increment,Decrement.

Addition:- When S1 and S0 = 0 0, the value of B is applied to the Y inputs of the adder. If Cin = 0, the output D = A + B. if Cin =1, output D = A + B + 1. Both cases perform the add micro operation with or without adding the input carry.
Subtraction:- When S1 and S0 = 0 1, the value of B is applied to the Y inputs of the adder. If Cin = 1, then D = A + B + 1. this produces A plus the 2’s complement of B, which is equivalent to a subtraction of A – B. when Cin = 0, then D = A + B. this is equivalent to a subtract with borrow, that is , A – B – 1.
Increment:- When S1 and S0 = 1 0, the inputs from B are neglected , and instead, all 0’s are inserted into the y inputs. The output becomes D = A + 0 + Cin. This gives D = A when Cin = 0 and D = A + 1 when Cin = 1. in the first case we have a direct transfer from the input A to output D. in the second case, the value of A is incremented by 1.
Decrement:- When S1 and S0 = 1 1, all 1’s are inserted into the Y inputs of the adder to produce the decrement operation D = A – 1 when Cin = 0. this is because a number with all 1’s is equal to the 2’s complement of 1 (the 2’s complement of binary 0001 is 1111). Adding number A to the 2’complement of 1 produces F = A + 2’s complement of 1 = A – 1 when Cin = 1, then D = A – 1 + 1 = A, which causes a direct transfer from input A to output D. NOTE :- Micro operation D = A is generated twice , so there are only 7 distinct Micro operations in the arithmetic circuit.3:Logic micro-operations:
These micro operations are used to perform bit style operations / manipulations on non numeric data.In computer central processing units, micro-operations are the functional or atomic, operations of a processor. These are low level instructions used in some designs to implement complex machine instructions. They generally perform operations on data stored in one or more registers.Logic micro operations are bit-wise operations, i.e., they work on the individual bits of data. These are useful for bit manipulations on binary data and also useful for making logical. decisions based on the bit value. There are, in principle, 16 different logic functions that can be defined over two binary input.

4: Shift micro operations:

They are used to perform shift operations in data store in registers.Shift Micro Operations in computer architecture are those which are used in serial shifting of data present in a register. We can also say that Shift micro Operations move or shift data in a register bit wise that is, one bit at a time either left or right from its original position.

In registers, there will occur conditions in order to manipulate data by shifting or moving the data bits either towards their left or towards their right and perform required operation. Suppose that addition should be performed on the data stored in two different registers and as the data is stored in binary form, shifting binary digits from left to right or vice-versa can result in the change of value in the register. If one wants to manipulate the data in the register by shifting the digits instead of clearing the register and assigning a new value to the register, we can use Shift Micro Operations.

Example: Let us take two values, 0 and 9 in two different registers A and B. We perform addition on both the registers before shift operation and after doing shift operation.

As we know that 0 has its binary value ‘0000’ and 9 as ‘1000’, and in registers binary values are stored. So if we add these two values, we get.

0000+1000=1000 (New value is 9 after addition without performing shift operation)

But, when we perform shift left operation, that is, shifting one bit towards left on 9, 1000 changes to 0000 as follows

So, after shifting one bit towards left, as shown in the above representation, a o will enter from the right end and one in the left most end will be removed from the 4 digit value. After shifting we get

So, if we add now, the result changes to zero as 9 changed to zero after shift left operation.

0000 (0 in register A)

+0000 (9 changed to 0 due to shift left operation performed on register B)

0000 (The value changed to be 0 instead of 9).

So, without the need of clearing the value first in the register and then inserting a new value, we directly change the value in the register by performing shift operation.

Types of Shift Micro Operations

Arithmetic Shift Micro Operation
Logical Shift Micro Operation
Circular Shift Micro Operation

1:Arithmetic Shift Micro Operation

Arithmetic Shift Operation shifts signed (positive or negative) binary numbers either left or right by multiplying or dividing by 2. For, Arithmetic Shift left micro operation, the value in the register is multiplied by 2 and whereas for Arithmetic Shift right micro operation, the value in the register is divided by 2.

In RTL (RTL stands for Register Transfer Language), we can represent this arithmetic shift micro operations as

R ← ashl R (arithmetic shift left R (register))

R ← ashr R (arithmetic shift right R (register))

Diagram showing Arithmetic shift left operation is as follows:

Diagram showing Arithmetic shift right operation is as follows:

2:Logical Shift Micro Operation

A Logical Shift Micro Operation transfers a 0 (zero) through the serial input, either from left or right depending on the type. For, logical shift left micro operation, 0 (zero) is transferred through the right of the data and for the logical shift right micro operation, 0 (zero is transferred through the left of the data as shown in the figures below.

R ← shl R (shift left register (R)).

R ← shr R (shift right register (R)).

Below is the diagram showing the logical shift right is as follows:

3:Circular Shift Micro Operation

A Circular Shift micro operation performs the shifting of bits from one end of the register to the other end of the register. In Circular shift left operation, the left most bit in the register is transferred to the right most end and in the circular shift right operation, the right most bit in the register is transferred or shifted to the left most end of the register as shown in the figures below:

R ← cil R (circular shift left register (R)).

R ← cir R (circular shift right register (R)).

Below is the diagram showing circular shift left micro operation