A-2
OPCODE MAP
DThe reg field of the ModR/M byte selects a debug register (for example,
MOV (0F21,0F23)).
EA ModR/M byte follows the opcode and specifies the operand. The operand is either a
general-purpose register or a memory address. If it is a memory address, the address is
computed from a segment register and any of the following values: a base register, an
index register, a scaling factor, a displacement.
FEFLAGS Register.
GThe reg field of the ModR/M byte selects a general register (for example, AX (000)).
IImmediate data. The operand value is encoded in subsequent bytes of the instruction.
JThe instruction contains a relative offset to be added to the instruction pointer register
(for example, JMP (0E9), LOOP).
MThe ModR/M byte may refer only to memory (for example, BOUND, LES, LDS, LSS,
LFS, LGS, CMPXCHG8B).
OThe instruction has no ModR/M byte; the offset of the operand is coded as a word or
double word (depending on address size attribute) in the instruction. No base register,
index register, or scaling factor can be applied (for example, MOV (A0A3)).
PThe reg field of the ModR/M byte selects a packed quadword MMX technology reg-
ister.
QA ModR/M byte follows the opcode and specifies the operand. The operand is either
an MMX technology register or a memory address. If it is a memory address, the ad-
dress is computed from a segment register and any of the following values: a base reg-
ister, an index register, a scaling factor, and a displacement.
RThe mod field of the ModR/M byte may refer only to a general register (for example,
MOV (0F20-0F24, 0F26)).
SThe reg field of the ModR/M byte selects a segment register (for example, MOV
(8C,8E)).
TThe reg field of the ModR/M byte selects a test register (for example, MOV
(0F24,0F26)).
VThe reg field of the ModR/M byte selects a packed SIMD floating-point register.
WAn ModR/M byte follows the opcode and specifies the operand. The operand is either
a SIMD floating-point register or a memory address. If it is a memory address, the ad-
dress is computed from a segment register and any of the following values: a base reg-
ister, an index register, a scaling factor, and a displacement
XMemory addressed by the DS:SI register pair (for example, MOVS, CMPS, OUTS, or
LODS).
YMemory addressed by the ES:DI register pair (for example, MOVS, CMPS, INS,
STOS, or SCAS).
