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Addressing mode specify the various ways in which value of operand is accessed . the purpose of an address field is to point to the current value V(x) of some operand X used by an instrution. the addressing mode of X effects the following issues .
(i) Immediate : the data (X) is eighter 8 bits or 16 bit long and part of the instrutions by implication X is constant , as it is undesirable to modify instruction field during excutions.
(ii) Direct : the n- bit effective address (EA) of data (X) is part of the instructions . thus X corresponds to a variables and its value V(x) can be varied is without modifying the instruction address field .
- the speed with which V(x) can be accessed by the CPU
- the ease with which V(x) can be specified and altered .
(i) Immediate : the data (X) is eighter 8 bits or 16 bit long and part of the instrutions by implication X is constant , as it is undesirable to modify instruction field during excutions.
(ii) Direct : the n- bit effective address (EA) of data (X) is part of the instructions . thus X corresponds to a variables and its value V(x) can be varied is without modifying the instruction address field .
Indirect : the effective address of data (x) is in the some other location. this is an useful when it required to change the loaction of X without changing the address field of amny instructions that refer to X .
types of address modes
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