M80C287 datasheet(2/29 Pages) INTEL

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M80C287

M80C287 Data Registers

64 63

R0 Sign

Exponent

Significand

Control Register

Instruction Pointer

Status Register

Data Pointer

Tag Word

Figure 2 M80C287 Register Set

FUNCTIONAL DESCRIPTION

The M80C287 Numeric Processor Extension (NPX)

provides arithmetic instructions for a variety of nu-

meric data types It also executes numerous built-in

transcendental functions (eg tangent sine cosine

and log functions) The M80C287 effectively ex-

tends the register and instruction set of the CPU for

existing data types and adds several new data types

as well Figure 2 shows the additional registers visi-

ble to programs in a system that includes the

M80C287 Essentially the M80C287 can be treated

as an additional resource or an extension to the

M80C286 CPU The M80C286 CPU together with an

M80C287 NPX can be used as a single unified sys-

tem

The M80C287 has two operating modes After reset

the M80C287 is in the real-address mode It can be

placed into protected mode by executing the

FSETPM instruction It can be switched back to real-

address mode by executing the FRSTPM instruction

(note that this feature is useful only with CPU’s that

can also switch back to real-address mode) These

instructions control the format of the administrative

instructions

FLDENV

FSTENV

FRSTOR

and

FSAVE Regardless of operating mode all refer-

ences to memory for numerics data or status infor-

mation are performed by the M80C286 CPU and

therefore obey the memory-management and pro-

tection rules of the M80C286 CPU

In real-address mode a system that includes the

M80C287 is completely upward compatible with

software for the M8086M8087 and for M80286

M80287 real-address mode

In protected mode

a system that includes the

M80C287 is completely upward compatible with

software for M80286M80287 protected mode sys-

tems

The only differences of operation that may appear

when M8086M8087 programs are ported to a pro-

tected-mode M80C287 system are in the format of

operands

for

the

administrative

instructions

FLDENV FSTENV FRSTOR and FSAVE These in-

structions are normally used only by exception han-

dlers and operating systems not by applications

programs

PROGRAMMING INTERFACE

The M80C287 adds to the CPU additional data

types registers instructions and interrupts specifi-

cally designed to facilitate high-speed numerics pro-

cessing To use the M80C287 requires no special

programming tools because all new instructions and

data types are directly supported by the assembler

and compilers for high-level languages All 8086

8088 development tools that support the M8087 can

also be used to develop software for the M80C286

M80C287 in real-address mode All M80286 devel-

opment tools that support the M80287 can also be

used to develop software for the M80C286

M80C287 The M80C287 supports all M387 NPX in-

structions producing the same binary results

All communication between the M80C286 CPU and

the M80C287 is transparent to applications soft-

ware The M80C286 CPU automatically controls the

M80C287 whenever a numerics instruction is exe-

cuted All physical memory and virtual memory of

the M80C286 CPU are available for storage of the

instructions and operands of programs that use the

M80C287 All memory addressing modes are avail-

able for addressing numerics operands

The instructions that the M80C287 adds to the in-

struction set are listed at the end of this data sheet

M80C287 Datasheet(PDF) 2 Page - Intel Corporation

M80C287 Datasheet(HTML) 2 Page - Intel Corporation

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