REGISTER TRANSFER LANGUAGE

•Combinational and sequential circuits can be used to create simple digital systems.

•These are  the low-level building blocks of a digital computer.

•Simple digital systems are frequently characterized in terms of

–the registers they contain, and

–the operations that they perform.

•Typically,

–What operations are performed on the data in the registers

–What information is passed between registers

•The operations executed on data stored in registers are called microoperations.

•Examples of microoperations

–Shift

–Load

–Clear

–Increment

–Count

MICROOPERATION

An elementary operation performed (during one clock pulse), on the information stored in one or more registers

REGISTER  TRANSFER  LANGUAGE

•The symbolic notation used to describe the microoperation transfers among registers is called a Register transfer language.

•Register transfer language

–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.

–Increment

–Count

Register  Transfer

•Registers are designated by capital letters, sometimes followed by numbers (e.g., A, R13, IR).

•Often the names indicate function:

–MAR  - memory address register

–PC  - program counter

–IR  - instruction register

•Information transfer from one register to another is designated in symbolic form by means of a replacement operator.

 

    R2  ß R1

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

•Often we want the transfer to occur only under a predetermined control condition.

   if (p=1) then (R2 ß R1)

      where p is a control signal generated in the control section.

•In digital systems, this is often done via a control signal, called a control function

–If the signal is 1, the action takes place

•This is represented as:

             P: R2 ¬ R1

Which means “if P = 1, then load the contents of register R1 into register R2”, i.e., if (P = 1)  then  (R2 ¬ R1)