ADDRESSING MODES AND FORMATS - Coggle Diagram
ADDRESSING MODES AND FORMATS
Address fields refers to a register rather than a main memory address
( EA = R )
are only small address fields is needed in the instruction and no time consuming memory references are required. The
is the address space is very limited.
Analogous to indirect address. The only difference is whether the address field refers to a memory location or a register
( EA = (R)
. Address space is limitation of the address field and it's uses one less memory references that indicate addressing
Refers to the address of a word in memory which contains a full-length address of the operand
is for the word length of N an address space of 2 power of n is now available. The
is instruction execute requires 2 memory references to fetch the operand.
Combines the capabilities of direct addressing & register indirect addressing
(EA =A + (R))
. Requires that the instruction have two address fields, at least one of which is explicit. Most common uses
relative addressing, Base-register addressing and indexing.
Address field contain contains the effective address of the operand. Effective address
(EA) = address field (A)
. Direct mode was common in earlier generations of computers. It only request only one memory reference and not special calculation. Limitation is that is provides only a limited address space.
A stack is a liner array of locations and a reversed block of locations. It is associated with the stack is a pointer whose value is the address of the top of the stack. The machine instruction need not include the memory reference but implicitly operate on the top of the stack.
Simplest mode. Can be used to define & use constants or set initial values or variable. The
is no memory reference other than the instruction fetch is required to obtain the operand. The
is the size of the number is restricted to the size of the address field.
Allocation of bits
Number of addressing, Number of operands, Register versus memory, Number of register sets, Address Range, Address Granularity.
Variation can be provided efficiently and compactly. It increase the complexity of the processor. It also does not remove the desirable of making all of the instruction lengths integrally that related to the to word lenght.
Most basic design issues. Affects, and is affected by
memory size, memory organization, Bus structure, Processor complexity, processor speed.
It should be equal to the memory-transfer length or one should be multiple of the other (8 bits).