Intel 80287 manual Appendix B 80286 Instruction SET

APPENDIX B

THE 80286 INSTRUCTION SET

This section presents the 80286 instruction set using Intel's ASM286 notation. All possible operand types are shown. Instructions are organized alphabetically according to generic operations. Within each operation, many different instructions are possible depending on the operand. The pages are presented in a standardized format, the elements of which are described in the following paragraphs.

Opeode

This column gives the complete object code produced for each form of the instruction. Where possible, the codes are given as hexadecimal bytes, presented in the order in which they will appear in memory, Several shorthand conventions are used for the parts of instructions which specify operands. These conventions are as follows:

In: (n is a digit from 0 through 7) A ModRM byte, plus a possible immediate and displacement field follow the opcode. See figure B-1 for the encoding of the fields. The digit n is the value of the REG field of the ModRM byte. To obtain the possible hexadecimal values for / n, refer to column n of table B-1. Each row gives a possible value for the effective address operand to the instruction. The entry at the end of the row indicates whether the effective address operand is a register or memory; if memory, the entry indicates what kind of indexing and/or displacement is used. Entries with D8 or Dl6 signify that a one-byte or two-byte displacement quantity immediately follows the ModRM and optional immediate field bytes. The signed displacement is added to the effective address offset.

I r: A ModRM byte that contains both a register operand and an effective address operand, followed by a possible immediate and displacement field. See figure B-2 for the encoding of the fields. The ModRM byte could be any value appearing in table B-1. The column determines which register operand was selected; the row determines the form of effective address. If the row entry mentions D8 or D 16, then a one-byte or two-byte displacement follows, as described in the previous paragraph.

cb: A one-byte signed displacement in the range of -128 to +127 follows the opcode. The displace- ment is sign-extended to 16 bits, and added modulo 65536 to the offset of the instruction FOLLOW- ING this instruction to obtain the new IP value.

cw: A two-byte displacement is added modulo 65536 to the offset of the instruction FOLLOWING this instruction to obtain the new IP value.

cd: A two-word pointer which will be the new CS:IP value. The offset is given first, followed by the selector.

db: An immediate byte operand to the instruction which follows the opcode and ModRM bytes. The opcode determines if it is a signed value.

dw: An immediate word operand to the instruction which follows the opcode and ModRM bytes. All words are given in the 80286 with the low-order byte first.

+rb: A register code from 0 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: AL=O, CL= 1, DL=2, BL=3, AH=4, CH=5, DH=6, and BH=7.

8-1