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.
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