Instruction Sets:Addressing Modes and formats

Addressing Modes and Formats

Immediate Addressing

Direct Addressing

Indirect Addressing 

Register Addressing

Register Indirect Addressing

•Operand is in memory cell pointed to by contents of register R

•Advantages and limitations- basically same as indirect addressign

•Address space limitation of the address field is overcome by having that field refer to a word-length location containing an address

•Uses one less memory reference than indirect addressing

                                                    Displacement Addressing

•Combines the capabilities of direct addressing and register indirect addressing

•EA = A + (R)

•Address field hold two values

—A = base value

—R = register that holds displacement

—or vice versa

•Most common uses:

—Relative addressing

—Base-register addressing