Basic operational concepts

-conn b/w the processor and memory

individual instructions are brought form the memory into the processor for a specific operation

data to be used as operands are also sotred in the memory

MAR = memory addr register - holds the addr loc to be accessed

MDR = memory data register - stores the data to read/write an addr

PC = program counter

IR = insrtuction register

operation steps

• execute a prog starts when pc is set to point the first instr of the prog

• contents of pc are transfered to MAR

• “read control signal” is sent to the memory

• addr word is read to memory and loaded to MDR

• contents of MDR are transferred to the IR and now decoded and executed

• if it is related to ALU also try to obtain the required operands

• when operand is read it is tranfered to ALU from MDR

• after a couple of repeated cycles the ALU can perform the desired operation

• result sent to MDR

• addr of the location of the result is stored to MAR & write cycle is initiated

• contents of the pc is incremented and points to next instruction/location

the decoded instr are stored to IR

instru eg:-> add LOCA,R0 = add the value of loca nad r0 and sotre it in r0

which registeers can interract with the secondary storage- MAR

During the executino of a prog PC is initilised

MAR is connected to Memory