80C187 datasheet(27/30 Pages) INTEL

27 / 30 page

80C187

80C187 EXTENSIONS TO THE CPU’s

INSTRUCTION SET

Instructions for the 80C187 assume one of the five

forms shown in Table 12 In all cases instructions

are at least two bytes long and begin with the bit

pattern 11011B which identifies the ESCAPE class

of instruction Instructions that refer to memory oper-

ands specify addresses using the CPU’s addressing

modes

MOD (Mode field) and RM (RegisterMemory spec-

ifier) have the same interpretation as the corre-

sponding fields of CPU instructions (refer to Pro-

grammer’s Reference Manual for the CPU) The

DISP (displacement) is optionally present in instruc-

tions that have MOD and RM fields Its presence

depends on the values of MOD and RM as for in-

structions of the CPU

The instruction summaries that follow assume that

the instruction has been prefetched decoded and is

ready for execution that bus cycles do not require

wait states that there are no local bus HOLD re-

quests delaying processor access to the bus and

that no exceptions are detected during instruction

execution Timings are given in internal 80C187

clocks and include the time for opcode and data

transfer between the CPU and the NPX If the in-

struction has MOD and RM fields that call for both

base and index registers add one clock

Table 12 Instruction Formats

Instruction

Optional

First Byte

Second Byte

Field

11011

OPA

MOD

OPB

DISP

11011

OPA

MOD

OPB

DISP

11011

OPA

OPB

ST (i)

11011

15–11

4 3

NOTES

OP e Instruction opcode possibly split into two fields OPA and OPB

MF e Memory Format

32-Bit Real

32-Bit Integer

64-Bit Real

16-Bit Integer

d e Destination

Destination is ST(0)

Destination is ST(i)

R XOR d e 0

Destination (op) Source

R XOR d e 1

Source (op) Destination

In FSUB and FDIV the low-order bit of OPB is the R (reversed) bit

P e Pop

Do not pop stack

Pop stack after operation

ESC e 11011

ST(i) e Register Stack Element

000 e Stack Top

001 e Second Stack Element

111 e Eighth Stack Element

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