The DICT Development Group

Search for:
Search type:

Database copyright information
Server information

1 definition found
 for addressing mode
From The Free On-line Dictionary of Computing (30 December 2018) :

  addressing mode
     1.  One of a set of methods for
     specifying the operand(s) for a machine code
     instruction.  Different processors vary greatly in the
     number of addressing modes they provide.  The more complex
     modes described below can usually be replaced with a short
     sequence of instructions using only simpler modes.
     The most common modes are "register" - the operand is stored
     in a specified register; "absolute" - the operand is stored
     at a specified memory address; and "{immediate" - the operand
     is contained within the instruction.
     Most processors also have indirect addressing modes, e.g.
     "register indirect", "memory indirect" where the specified
     register or memory location does not contain the operand but
     contains its address, known as the "{effective address".  For
     an absolute addressing mode, the effective address is
     contained within the instruction.
     Indirect addressing modes often have options for pre- or post-
     increment or decrement, meaning that the register or memory
     location containing the effective address is incremented or
     decremented by some amount (either fixed or also specified in
     the instruction), either before or after the instruction is
     executed.  These are very useful for stacks and for
     accessing blocks of data.  Other variations form the effective
     address by adding together one or more registers and one or
     more constants which may themselves be direct or indirect.
     Such complex addressing modes are designed to support access
     to multidimensional arrays and arrays of data structures.
     The addressing mode may be "implicit" - the location of the
     operand is obvious from the particular instruction.  This
     would be the case for an instruction that modified a
     particular control register in the CPU or, in a stack based
     processor where operands are always on the top of the stack.
     IBM+System+370/{XA">2. In IBM System 370/{XA the addressing mode bit controls
     the size of the effective address generated.  When this bit
     is zero, the CPU is in the 24-bit addressing mode, and 24 bit
     instruction and operand effective addresses are generated.
     When this bit is one, the CPU is in the 31-bit addressing
     mode, and 31-bit instruction and operand effective addresses
     are generated.
     ["IBM System/370 Extended Architecture Principles of
     Operation", Chapter 5., 'Address Generation', BiModal

Contact=webmaster@dict.org Specification=RFC 2229