The operand is in a memory location referenced by an effective
address computed by adding together the PC
a second data or address register, and an optional displacement.
The displacement can be none, or 16bit or 32bit wide.
The value in the second register can either be a full long word or a sign-
extended word value. This is specified by a .W or .L extension after
the register. If no extension is used, the assembler assumes a word
The Index register can optionally be multiplied with 1, 2, 4, or 8
As INDEX register can be used A0 .. A7 or D0 .. D7