80C187 datasheet(13/30 Pages) INTEL

13 / 30 page

80C187

and exception When loading a signalling NaN

FLD

singledouble precision signals an invalid-

operand exception

16 The 80C187 only generates quiet NaNs (as on

the 8087) however the 80C187 distinguishes

between quiet NaNs and signalling NaNs Sig-

nalling NaNs trigger exceptions when they are

used as operands quiet NaNs do not (except for

FCOM FIST and FBSTP which also raise IE for

quiet NaNs)

17 When stack overflow occurs during FPTAN and

overflow is masked both ST(0) and ST(1) con-

tain quiet NaNs The 8087 leaves the original

operand in ST(1) intact

18 When the scaling factor is g % the FSCALE

(ST(0)

ST(1) instruction behaves as follows

(ST(0) and ST(1) contain the scaled and scaling

operands respectively)

FSCALE (0 %) generates the invalid opera-

tion exception

FSCALE (finite b%) generates zero with the

same sign as the scaled operand

FSCALE (finite a %) generates % with the

same sign as the scaled operand

The 8087 returns zero in the first case and rais-

es the invalid-operation exception in the other

cases

19 The 80C187 returns signed infinityzero as the

unmasked response to massive overflowunder-

flow The 8087 supports a limited range for the

scaling factor within this range either massive

overflowunderflow do not occur or undefined

results are produced

Table 7 Pin Summary

Function

Active

Input

Name

State

Output

CLK

CLocK

CKM

ClocKing Mode

RESET

System reset

High

PEREQ

Processor Extension

High

REQuest

BUSY

Busy status

High

ERROR

Error status

Low

D15–D0

Data pins

High

NPRD

Numeric Processor ReaD

Low

NPWR

Numeric Processor WRite

Low

NPS1

NPX select

Low

NPS2

NPX select

High

CMD0

CoMmanD 0

High

CMD1

CoMmanD 1

High

VCC

System power

VSS

System ground

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