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Instruction Set Summary
A-2
Table A-1
V ariables Used In Instruc tion Set S ummary Tables
Variable
d
Function
Specifies direction.
Values Description
0
to r/m
1
to reg
data-8
data-low
data-high
data-SX
Specifies a non-address constant data used by the
instruction. The "8" indicates an 8-bit constant; "low",
the low-order byte of a 16-bit constant; "high", the
high order byte of a 16-bit constant; and "SX", an 8-
bit constant that is sign-extended for a 16-bit
operation.
Specifies the displacement. The "8" indicates an 8-
bit displacement; "low", the low-order byte of a 16-bit
displacement; and "high", the high-order byte of a 16-
bit displacement. For some forms of MOV, specifies
a 0-relative address.
Along with r/m, determines the effective address of
the memory operand.
disp-8
disp-low
disp-high
mod
11
00
01
10
000
001
010
011
100
101
110
111
000
r/mis treated as a regfield
DISP = 0, disp-low and disp-high are absent
DISP = disp-low sign-extended to 16-bits, disp-high is absent
DISP = disp-high: disp-low
EA = (BX)+(SI)+DISP
EA = (BX)+(DI)+DISP
EA = (BP)+(SI)+DISP
EA = (BP)+(DI)+DISP
EA = (SI)+DISP
EA = (DI)+DISP
EA = (BP)+DISP (except if mod=00, then EA = disp-high:disp:low)
EA = (BX)+DISP
AL, if w=0 or implicit 8-bit
AX, if w=1 or implicit 16-bit
CL, if w=0 or implicit 8-bit
CX, if w=1 or implicit 16-bit
DL, if w=0 or implicit 8-bit
DX, if w=1 or implicit 16-bit
BL, if w=0 or implicit 8-bit
BX, if w=1 or implicit 16-bit
AH, if w=0 or implicit 8-bit
SP, if w=1 or implicit 16-bit
CH, if w=0 or implicit 8-bit
BP, if w=1 or implicit 16-bit
DH, if w=0 or implicit 8-bit
SI, if w=1 or implicit 16-bit
BH, if w=0 or implicit 8-bit
DI, if w=1 or implicit 16-bit
no sign extension
sign-extend (for 16-bit operations only, w=1)
r/m
Along with mod determines the effective address of
the memory operand.
reg
Represents a register, and is assigned according to
the value of wand reg
001
010
011
100
101
110
111
s
Specifies immediate operand sign-extension.
0
1
seg-low
seg-high
Specifies the segment base address value.
Represents the high-order 16 bits of a 20-bit address,
with an implicit 4 low-order 0 bits.
Specifies a segment register.
sreg
00
01
10
11
0
1
ES register
CS register
SS register
DS register
8-bit value
16-bit value
w
Specifies an 8- or 16-bit value.
XXX YYY
Specifies opcode to proc. ext.
Notes:
1 – DISP follows the operand address (before data if required).
2 – The physical addresses of all operands addressed by the BP register are computed using the SS segment register. The physical addresses
of the destination operands of the string primitive operations (those addressed by the DI register) are computed using the ES segment, which
cannot be overridden.