Appendix d instruction set opcodes and clock cycle, Table d1. operand variables, Table d-1. operand variables – Intel 80C188XL User Manual

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D-1

APPENDIX D

INSTRUCTION SET OPCODES

AND CLOCK CYCLES

This appendix provides reference information for the 80C186 Modular Core family instruction
set. Table D-1 defines the variables used in Table D-2, which lists the instructions with their for-
mats and execution times. Table D-3 is a guide for decoding machine instructions. Table D-4 is
a guide for encoding instruction mnemonics, and Table D-5 defines Table D-4 abbreviations.

Table D-1. Operand Variables

Variable

Description

mod

mod and r/m determine the Effective Address (EA).

r/m

r/m and mod determine the Effective Address (EA).

reg

reg represents a register.

MMM

MMM and PPP are opcodes to the math coprocessor.

PPP

PPP and MMM are opcodes to the math coprocessor.

TTT

TTT defines which shift or rotate instruction is executed.

r/m

EA Calculation

mod

Effect on EA Calculation

0 0 0

(BX) + (SI) + DISP

0 0

if r/m

≠

110, DISP = 0; disp-low and disp-high are absent

0 0 1

(BX) + (DI) + DISP

0 0

if r/m = 110, EA = disp-high:disp-low

0 1 0

(BP) + (SI) + DISP

0 1

DISP = disp-low, sign-extended to 16 bits; disp-high is absent

0 1 1

(BP) + (DI) + DISP

1 0

DISP = disp-high:disp-low

1 0 0

(SI) + DISP

1 1

r/m is treated as a reg field

1 0 1

(DI) + DISP

DISP follows the second byte of the instruction (before any required data).

Physical addresses of operands addressed by the BP register are computed
using the SS segment register. Physical addresses of destination operands of
string primitives (addressed by the DI register) are computed using the ES seg-
ment register, which cannot be overridden.

1 1 0

(BP) + DISP, if mod

≠

disp-high:disp-low, if mod =00

1 1 1

(BX) + DISP

reg

16-bit (w=1)

8-bit (w=0)

TTT

Instruction