OPCODE MAP

A.3.5 Escape Opcode Instructions

Opcode maps for coprocessor escape instruction opcodes (x87 floating-point instruction opcodes) are in Table A-8 through Table A-23. These maps are grouped by the first byte of the opcode, from D8-DF. Each of these opcodes has a ModR/M byte. If the ModR/M byte is within the range of 00H-BFH, bits 3-5 of the ModR/M byte are used as an opcode extension, similar to the technique used for 1-and 2-byte opcodes (see Section A.3.4). If the ModR/M byte is outside the range of 00H through BFH, the entire ModR/M byte is used as an opcode extension.

Example A-3. Opcode with ModR/M Byte in the 00H through BFH Range

DD0504000000H can be interpreted as follows:

•The instruction encoded with this opcode can be located in Section A.3.5.6. Since the ModR/M byte (05H) is within the 00H through BFH range, bits 3 through 5 (000) of this byte indicate the opcode for an FLD double-real instruction (see Table A-10).

•The double-real value to be loaded is at 00000004H (the 32-bit displacement that follows and belongs to this opcode).

Example A-4. Opcode with ModR/M Byte outside the 00H through BFH Range

D8C1H can be interpreted as follows:

•This example illustrates an opcode with a ModR/M byte outside the range of 00H through BFH. The instruction can be located in Section A.3.4.

•In Table A-9, the ModR/M byte C1H indicates row C, column 1 (the FADD instruction using ST(0), ST(1) as operands).

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OPCODE MAP

A.3.5.1 ESCAPE OPCODES WITH D8 AS FIRST BYTE

Table A-8 and Table A-9 contain opcode maps for the escape instruction opcodes that begin with D8H. Table A-8 shows the opcode map if the accompanying ModR/M byte within the range of 00H-BFH. Here, the value of bits 3-5 (nnn field in Figure A-1) selects the instruction.

Table A-8. D8 Opcode Map When ModR/M Byte is Within 00H to BFH†

nnn Field of ModR/M Byte

NOTES:

†All blanks in the opcode map are reserved and must not be used. Do not depend on the operation of undefined or reserved opcodes.

Table A-9 shows the opcode map if the accompanying ModR/M byte is outside the range of 00H-BFH. Here, the first digit of the ModR/M byte selects the row in the table and the second digit selects the column.

Table A-9. D8 Opcode Map When ModR/M Byte is Outside 00H to BFH†

NOTES:

†All blanks in the opcode map are reserved and must not be used. Do not depend on the operation of undefined or reserved opcodes.

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OPCODE MAP

A.3.5.2 ESCAPE OPCODES WITH D9 AS FIRST BYTE

Table A-10 and Table A-11 contain opcode maps for escape instruction opcodes that begin with D9H. Table A-10 shows the opcode map if the accompanying ModR/M byte is within the range of 00H-BFH. Here, the value of bits 3-5 (nnn field in Figure A-1) selects the instruction.

Table A-10. D9 Opcode Map When ModR/M Byte is Within 00H to BFH†

nnn Field of ModR/M Byte

NOTE:

†All blanks in the opcode map are reserved and must not be used. Do not depend on the operation of undefined or reserved opcodes.

Table A-11 shows the opcode map if the accompanying ModR/M byte is outside the range of 00H-BFH. Here, the first digit of the ModR/M byte selects the row in the table and the second digit selects the column.

Table A-11. D9 Opcode Map When ModR/M Byte is Outside 00H to BFH†

NOTES:

†All blanks in the opcode map are reserved and must not be used. Do not depend on the operation of undefined or reserved opcodes.

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OPCODE MAP

A.3.5.3 ESCAPE OPCODES WITH DA AS FIRST BYTE

Table A-12 and Table A-13 contain the opcode maps for the escape instruction opcodes that begin with DAH. Table A-12 shows the opcode map if the accompanying ModR/M byte within the range of 00H-BFH. Here, the value of bits 3-5 (nnn field in Figure A-1) selects the instruction.

Table A-12. DA Opcode Map When ModR/M Byte is Within 00H to BFH†

nnn Field of ModR/M Byte

NOTES:

†All blanks in the opcode map are reserved and must not be used. Do not depend on the operation of undefined or reserved opcodes.

Table A-13 shows the opcode map if the accompanying ModR/M byte is outside the range of 00H-BFH. Here, the first digit of the ModR/M byte selects the row in the table and the second digit selects the column.

Table A-13. DA Opcode Map When ModR/M Byte is Outside 00H to BFH†

NOTES:

†All blanks in the opcode map are reserved and must not be used. Do not depend on the operation of undefined or reserved opcodes.

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