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Register Transfer Language (RTL)

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  • Difficulty Level : Medium
  • Last Updated : 11 Feb, 2022

In symbolic notation, it is used to describe the micro-operations transfer among registers. It is a kind of intermediate representation (IR) that is very close to assembly language, such as that which is used in a compiler.The term “Register Transfer” can perform micro-operations and transfer the result of operation to the same or other register. 

Micro-operations : 
The operation executed on the data store in registers are called micro-operations. They are detailed low-level instructions used in some designs to implement complex machine instructions. 

Register Transfer : 
The information transformed from one register to another register is represented in symbolic form by replacement operator is called Register Transfer. 

Replacement Operator : 
In the statement, R2 <- R1, <- acts as a replacement operator. This statement defines the transfer of content of register R1 into register R2. 

There are various methods of RTL – 

 

  1. General way of representing a register is by the name of the register enclosed in a rectangular box as shown in (a). 
     
  2. Register is numbered in a sequence of 0 to (n-1) as shown in (b). 
     
  3. The numbering of bits in a register can be marked on the top of the box as shown in (c). 
     
  4. A 16-bit register PC is divided into 2 parts- Bits (0 to 7) are assigned with lower byte of 16-bit address and bits (8 to 15) are assigned with higher bytes of 16-bit address as shown in (d). 
     

 

Basic symbols of RTL : 

SymbolDescriptionExample
Letters and NumbersDenotes a RegisterMAR, R1, R2
( )Denotes a part of register

R1(8-bit)

R1(0-7)

<-Denotes a transfer of informationR2 <- R1
,Specify two micro-operations of Register Transfer

R1 <- R2

R2 <- R1

:Denotes conditional operations

P : R2 <- R1

if P=1

Naming Operator (:=)Denotes another name for an already existing register/aliasRa := R1

Register Transfer Operations:

The operation performed on the data stored in the registers are referred to as register transfer operations.

There are different types of register transfer operations:

1. Simple Transfer – R2 <- R1

 The content of R1 are copied into R2 without affecting the content of R1. It is an unconditional type of transfer operation. 

2. Conditional Transfer – 

It indicates that if P=1, then the content of R1 is transferred to R2. It is a unidirectional operation. 

3. Simultaneous Operations – 
If 2 or more operations are to occur simultaneously then they are separated with comma (,)

 

If the control function P=1, then load the content of R1 into R2 and at the same clock load the content of R2 into R1.
 

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