What Is Register Transfer Level

Registers in Computer Compages

A Register is a grouping of flip-flops with each flip-flop capable of storing i bit of information. An n-fleck register has a group of north flip-flops and is capable of storing binary information of n-bits.

If yous are not familiar with logic gates concepts, you lot can acquire information technology from hither.

A register consists of a group of flip-flops and gates. The flip-flops hold the binary data and gates command when and how new information is transferred into a register. Diverse types of registers are available commercially. The simplest register is one that consists of merely flip-flops with no external gates.

These days registers are besides implemented every bit a register file.

Loading the Registers

The transfer of new information into a annals is referred to equally loading the register. If all the $.25 of register are loaded simultaneously with a common clock pulse than the loading is said to be done in parallel.

Register Transfer Linguistic communication

The symbolic annotation used to describe the micro-operation transfers amongst registers is chosen Register transfer linguistic communication.

The term register transfer ways the availability of hardware logic circuits that tin perform a stated micro-operation and transfer the upshot of the performance to the same or another register.

The discussion linguistic communication is borrowed from programmers who apply this term to programming languages. This programming linguistic communication is a process for writing symbols to specify a given computational process.

Following are some normally used registers:

Accumulator: This is the most mutual register, used to store data taken out from the retentiveness.
General Purpose Registers: This is used to shop data intermediate results during program execution. It can be accessed via associates programming.
Special Purpose Registers: Users practise non admission these registers. These registers are for Figurer system,

MAR: Memory Address Annals are those registers that holds the address for retention unit.
MBR: Memory Buffer Register stores instruction and information received from the memory and sent from the memory.
PC: Program Counter points to the next instruction to be executed.
IR: Instruction Register holds the instruction to exist executed.

Register Transfer

Data transferred from i annals to another is designated in symbolic class by means of replacement operator.

R2 ← R1

It denotes the transfer of the data from annals R1 into R2.

Normally we want the transfer to occur just in predetermined control condition. This tin can be shown by post-obit if-then statement: if (P=1) and then (R2 ← R1)

Here P is a control indicate generated in the control section.

Control Part

A control function is a Boolean variable that is equal to i or 0. The control part is shown equally:

P: R2 ← R1

The command condition is terminated with a colon. It shows that transfer operation can exist executed but if P=ane.

Micro-Operations

The operations executed on data stored in registers are called micro-operations. A micro-operation is an uncomplicated operation performed on the information stored in i or more registers.

Example: Shift, count, clear and load.

Types of Micro-Operations

The micro-operations in digital computers are of 4 types:

Annals transfer micro-operations transfer binary information from one register to some other.
Arithmetics micro-operations perform arithmetic operations on numeric information stored in registers.
Logic micro-operations perform bit manipulation operation on not-numeric data stored in registers.
Shift micro-operations perform shift micro-operations performed on data.

Arithmetic Micro-Operations

Some of the basic micro-operations are addition, subtraction, increment and decrement.

Add together Micro-Operation

It is defined past the following statement:

          R3 → R1 + R2

The to a higher place statement instructs the data or contents of register R1 to exist added to data or content of register R2 and the sum should be transferred to register R3.

Subtract Micro-Operation

Let united states over again take an example:

          R3 → R1 + R2' + 1

In subtract micro-operation, instead of using minus operator we have 1'southward compliment and add 1 to the register which gets subtracted, i.east R1 - R2 is equivalent to R3 → R1 + R2' + 1

Increment/Decrement Micro-Operation

Increment and decrement micro-operations are generally performed by adding and subtracting 1 to and from the annals respectively.

          R1 → R1 + 1

          R1 → R1 – 1

Symbolic Designation	Description
R3 ← R1 + R2	Contents of R1+R2 transferred to R3.
R3 ← R1 - R2	Contents of R1-R2 transferred to R3.
R2 ← (R2)'	Compliment the contents of R2.
R2 ← (R2)' + 1	2'due south compliment the contents of R2.
R3 ← R1 + (R2)' + ane	R1 + the 2'due south compliment of R2 (subtraction).
R1 ← R1 + i	Increment the contents of R1 by one.
R1 ← R1 - 1	Decrement the contents of R1 by one.

Logic Micro-Operations

These are binary micro-operations performed on the bits stored in the registers. These operations consider each fleck separately and treat them as binary variables.

Permit us consider the X-OR micro-operation with the contents of two registers R1 and R2.

          P: R1 ← R1 Ten-OR R2

In the to a higher place argument nosotros have also included a Command Office.

Assume that each register has iii bits. Allow the content of R1 exist 010 and R2 be 100. The X-OR micro-operation will be:

Shift Micro-Operations

These are used for serial transfer of data. That means we tin shift the contents of the register to the left or correct. In the shift left performance the serial input transfers a bit to the right most position and in shift right operation the series input transfers a bit to the left nearly position.

There are iii types of shifts every bit follows:

a) Logical Shift

It transfers 0 through the serial input. The symbol "shl" is used for logical shift left and "shr" is used for logical shift right.

          R1 ← she R1

          R1 ← she R1

The register symbol must be same on both sides of arrows.

b) Round Shift

This circulates or rotates the $.25 of register effectually the two ends without whatever loss of data or contents. In this, the serial output of the shift register is connected to its series input. "cil" and "cir" is used for circular shift left and right respectively.

c) Arithmetic Shift

This shifts a signed binary number to left or correct. An arithmetic shift left multiplies a signed binary number by 2 and shift left divides the number by two. Arithmetics shift micro-performance leaves the sign bit unchanged because the signed number remains same when it is multiplied or divided by 2.

Arithmetic Logical Unit

Instead of having private registers performing the micro-operations, reckoner system provides a number of registers connected to a common unit of measurement called as Arithmetics Logical Unit (ALU). ALU is the master and ane of the most important unit inisde CPU of figurer. All the logical and mathematical operations of computer are performed hither. The contents of specific register is placed in the in the input of ALU. ALU performs the given operation and then transfer it to the destination register.