The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson

2-22

THE

x86 MICROPROCESSORS

MOD REG R/M

0 0110111

Byte 2

For the second byte, MOD = 00 corresponding to [BX]. The register bits are 110 for DH

and R/M = 111 from Table 2.5. Thus, the instruction code is 88 37H.

vi) MOV AL, [SI][BX]

OPCODE

DW

10001010

Byte 1

MOD REGR/M

0 0000000

Byte 2

By following the same procedure as discussed for the previous instructions, the code for

this is 8A 00 H.

vii) ADD AX, 53H [SI][BX]

OPCODE

DW

00000011

Byte 1

MOD REG R/M

0 1000000

Byte 2

The third byte of the instruction is 53H, being the 8-bit displacement given in the instruc-

tion. Thus, the code is 03 40 53 H.

Segment Override Prefix

viii) MOV CS: [BX], DH

The segment over ...