Intel 80286, 80287 manual Instruction

THE 80286 INSTRUCTION SET

+rw: A register code from °through 7 which is added to the hexadecimal byte given at the left of the plus sign to form a single opcode byte~ The codes are: AX=O, CX=I, DX=2, BX=3, SP=4, BP=5, SI=6, and DI=7.

Instruction

This column gives the instruction mnemonic and possible operands. The type of operand used will determine the opcode and operand encodings. The following entries list the type of operand which can be encoded in the format shown in the instruction column. The Intel convention is to place the desti- nation operand as the left hand operand. Source-only operands follow the destination operand.

In many cases, the same instruction can be encoded several ways. It is recommended that you use the shortest encoding. The short encodings are provided to save memory space.

cb: a destination instruction offset in the range of 128 bytes before the end of this instruction to 127 bytes after the end of this instruction.

cw: a destination offset within the same code segment as this instruction. Some instructions allow a short form of destination offset. See cb type for more information.

cd: a destination address, typically in a different code segment from this instruction. Using the cd: address form with call instructions saves the code segment selector.

db: a signed value between -128 and +127 inclusive which is an operand of the instruction. For instructions in which the db is to be combined in some way with a word operand, the immediate value is sign"extended to form a word. The upper byte of the word is filled with the topmost bit of the immediate value.

dw: an immediate word value which is an operand ofthe instruction.

eb: a byte-sized oPllrand. This is either a byte register or a (possibly indexed) byte memory variable. Either operand location may be encoded in the ModRM field. Any memory addressing mode may be used.

ed: a memory-based pointer operand. Any memory addressing mode may be used. Use of a register addressing mode will cause exception 6.

ew: a word-sized operand. This is either a word register or a (possibly index!!d) word memory variable. Either operand location may be encoded in the ModRM field. Any memory 'addressing mode may be used.

m:a memory location. Operands in registers do not have a memory address. Any memory addressing mode may be used. Use of a register addressing mode will cause exception 6.

mb: a memory-based byte-sized operand. Any memory addressing mode may be used.

mw: a memory-based word operand. Any memory addressing mode may be used.

rb: one of the byte registers AL, CL, DL, BL, AH, CH, DH, or BH; rb has the value 0,1,2,3,4,5,6,

and 7, respectively. . "

rw: one of the word registers AX,CX, DX, BX, SP, BP, SI, or DI; rw has the value 0,1,2,3,4,5,6; and 7, respectively.

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