80C187 datasheet(11/30 Pages) INTEL

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80C187

Table 6 Exceptions

Exception

Cause

Default Action

(If Exception is Masked)

Invalid

Operation on a signalling NaN

Result is a quiet NaN

Operation

unsupported format indeterminate

integer indefinite or

form (0 % 00) (a %)

BCD indefinite

(b %) etc) or stack

overflowunderflow (SF is also set)

Denormalized

At least one of the operands is

The operand is normalized

Operand

denormalized ie it has the smallest

and normal processing

exponent but a nonzero significand

continues

Zero Divisor

The divisor is zero while the dividend

Result is %

is a noninfinite nonzero number

Overflow

The result is too large in magnitude

Result is largest finite

to fit in the specified format

value or %

Underflow

The true result is nonzero but too small

Result is denormalized

to be represented in the specified format and

or zero

if underflow exception is masked denormalization

causes loss of accuracy

Inexact

The true result is not exactly representable

Normal processing

Result

in the specified format (eg 13)

continues

(Precision)

the result is rounded according to the

rounding mode

Initialization

After FNINIT or RESET the control word contains

the value 037FH (all exceptions masked precision

control 64 bits rounding to nearest) the same values

as in an 8087 after RESET For compatibility with the

8087 the bit that used to indicate infinity control (bit

12) is set to zero however regardless of its setting

infinity is treated in the affine sense After FNINIT or

RESET the status word is initialized as follows

All exceptions are set to zero

Stack TOP is zero so that after the first push the

stack top will be register seven (111B)

The condition code C3–C0 is undefined

The B-bit is zero

The tag word contains FFFFH (all stack locations

are empty)

80C18680C187 initialization software should exe-

cute an FNINIT instruction (ie an FINIT without a

preceding WAIT) after RESET The FNINIT is not

strictly required for 80C187 software

but Intel

recommends its use to help ensure upward compati-

bility with other processors

8087 Compatibility

This section summarizes the differences between

the 80C187 and the 8087 Many changes have been

designed into the 80C187 to directly support the

IEEE standard in hardware These changes result in

increased performance by elminating the need for

software that supports the standard

GENERAL DIFFERENCES

The 8087 instructions FENIFNENI and FDISI

FNDISI perform no useful function in the 80C187

Numeric Processor Extension They do not alter the

state of the 80C187 Numeric Processor Extension

(They are treated similarly to FNOP except that

ERROR is not checked) While 80868087 code

containing these instructions can be executed on

the 80C18680C187 it is unlikely that the exception-

handling routines containing these instructions will

be completely portable to the 80C187 Numeric Proc-

essor Extension

The 80C187 differs from the 8087 with respect to

instruction data and exception synchronization Ex-

cept for the processor control instructions all of the

80C187 numeric instructions are automatically syn-

chronized by the 80C186 CPU When necessary the

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