INTEL387TMDX View Datasheet(PDF) - Intel

Part Name

Description

Manufacturer

INTEL387TMDX

Intel387™ DX MATH COPROCESSOR

Intel 

Intel387TM DX MATH COPROCESSOR

2 7 8087 and 80287 Compatibility

This section summarizes the differences between

the Intel387 DX MCP and the 80287 Any migration

from the 8087 directly to the Intel387 DX MCP must

also take into account the differences between the

8087 and the 80287 as listed in Appendix A

Many changes have been designed into the Intel387

DX MCP to directly support the IEEE standard in

hardware These changes result in increased per-

formance by eliminating the need for software that

supports the standard

2 7 1 GENERAL DIFFERENCES

The Intel387 DX MCP supports only affine closure

for infinity arithmetic not projective closure Bit 12 of

the Control Word (CW) no longer defines infinity

control It is a reserved bit but it is initialized to zero

after RESET or FINIT and is changeable upon load-

ing the CW Programs must ignore this bit

Operands for FSCALE and FPATAN are no longer

restricted in range (except for g %) F2XM1 and

FPTAN accept a wider range of operands

The results of transcendental operations may be

slightly different from those computed by 80287

In the case of FPTAN the Intel387 DX MCP supplies

a true tangent result in ST(1) and (always) a floating

point 1 in ST

Rounding control is in effect for FLD constant

Software cannot change entries of the tag word to

values (other than empty) that do not reflect the ac-

tual register contents

After reset FINIT and incomplete FPREM the In-

tel387 DX MCP resets to zero the condition code

bits C3 – C0 of the status word

In conformance with the IEEE standard the Intel387

DX MCP does not support the special data formats

pseudozero pseudo-NaN pseudoinfinity and un-

normal

Table 2 7 Exceptions

Exception

Cause

Invalid

Operation

Denormalized

Operand

Zero Divisor

Overflow

Underflow

Inexact

Result

(Precision)

Operation on a signaling NaN unsupported format

indeterminate form (0 % 0 0 (a %) a (b %) etc ) or

stack overflow underflow (SF is also set)

At least one of the operands is denormalized i e it has

the smallest exponent but a nonzero significand

The divisor is zero while the dividend is a noninfinite

nonzero number

The result is too large in magnitude to fit in the specified

format

The true result is nonzero but too small to be

represented in the specified format and if underflow

exception is masked denormalization causes loss of

accuracy

The true result is not exactly representable in the

specified format (e g 1 3) the result is rounded

according to the rounding mode

Default Action

(if exception is masked)

Result is a quiet NaN integer

indefinite or BCD indefinite

Normal processing

continues

Result is %

Result is largest finite value

or %

Result is denormalized or

zero

Normal processing

continues

16

16

Share Link: