INSTRUCTIONS AND INSTRUCTION SEQUENCING

  INSTRUCTIONS AND INSTRUCTION SEQUENCING 

A computer must have instructions capable of performing four types of operations

1. Data transfers between the main memory and the CPU registers
2. Arithmetic and logic operations on data
3. Program sequencing and control
4. I/O transfers

Notations used:-

Register Transfer Notation (RTN)            
Possible locations involved in transfer of information are memory location, CPU registers or registers in the I/O subsystem. We identify the names for the addresses of memory location as LOC, PLACE, A, VAR2 etc and the names for CPU registers as R0, R5 etc. The contents of a location or a register are denoted by placing the corresponding name between square brackets.

            

E.g.             R1 ← [LOC]               means that the contents of memory location LOC are

transferred into register R1.

   R3 ← [R1] + [R2]       adds the contents of registers R1 and R2 and then

places their sum into register R3.

             

Assembly Language Notation

The same operations can be represented in assembly language format as shown below.

E.g.             Move   LOC, R1

                    Add     R1,R2,R3