Data Organization and Addressing Capabilities
MOTOROLA MC68030 USER’S MANUAL 2-33
It is useful to examine the derived addressing modes available to a programmer (without
regard to the MC68030 effective addressing mode actually encoded) because the
programmer need not be concerned about these decisions. The assembler can choose the
more efficient addressing mode to encode.
In the list of derived addressing modes that follows, common programming terms are used.
The following definitions apply:
pointer — long-Word value in a register or in memory which represents an
address.
base — A pointer combined with a displacement to represent an address.
index — A constant or variable value added into an effective address calcula-
tion. A constant index is a displacement. A variable index is always
represented by a register containing the value.
disp — Displacement, a constant index.
subscript — The use of any of the data or address registers as a variable index
subscript into arrays of items 1, 2, 4 or 8 bytes in size.
relative — An address calculated from the program counter contents. The
address is position independent and is in program space. All other
addresses but psaddr are in data space.
addr — An absolute address.
psaddr — An absolute address in program space. All other addresses but PC
relative are in data space.
preindexed — All modes from absolute address through program counter relative.
postindexed— Any of the following modes:
addr — Absolute address in data space
psaddr,ZPC — Absolute address in program space
An — Register pointer with constant displacement
disp.An — Register pointer with constant displacement
addr,An — Absolute address with single variable name
disp,Pc — Simple PC relative
The addressing modes defined in programming terms, which are derivations of the
addressing modes provided by the MC68030 architecture, are as follows:
Immediate Data — #data:
The data is a constant located in the instruction stream.
Register Direct — Rn:
The contents of a register contain the operand.
Scanning Modes:
(An)+
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