Basic Operational Concepts in CAO

     

                     Figure : Connections between the processor and the  memory.

 

•  Programs reside in the memory through input devices

•  PC is set to point to the first instruction

•  The contents of PC are transferred to MAR

•  A Read signal is sent to the memory

•  The first instruction is read out and loaded into MDR

•  The contents of MDR are transferred to IR

•  Decode and execute the instruction

 

•Get operands for ALU

- General-purpose register

- Memory (address to MAR – Read – MDR to ALU)

 

•  Perform operation in ALU

 

•  Store the result back

- To general-purpose register

- To memory (address to MAR, result to MDR – Write)

 

•  During the execution, PC is incremented to the next instruction

 

     For Ex. 

  

               Add LOCA, R0

•Add the operand at memory location LOCA to the operand in a register R0 in the processor.

 

•Place the sum into register R0..

 

•Instruction is fetched from the memory into the processor

 

•The operand at LOCA is fetched and added to the contents of

  R0 – the resulting sum is stored in register R0.