8028x > IntelC80287-3
Modified: April 9, 2005, 2:52 am
Data Code:8620
Package:40CDIP w/ Gold Lid
Process:1.5 Micron
Architecture:80 bit FPU
Used in:Computers
Description:Intel 80287 is a co-processor for 80286 family of
processors. The 80287 has architecture similar to
Intel 8087, and it's completely object-code
compatible with the 8087 (but not pin-
compatible). The number of instructions and
execution time of instructions for both co-
processors is about the same. There are some
differences between the 80287 and 8087 FPUs:

The 80287 may run asynchronously from the main
processor. The 80286 processor divides external
clock by 2, while the co-processor divides it by
3. If both the 80286 and 80287 use the same
external clock it results in the co-processor
running at the 2/3 speed of the main processor.

When the main processor executes the FP
instructions it now checks if the co-processor is
busy, and, if necessary, will wait for the co-
processor to become available. As a result, it's
no longer necessary to add WAIT (FWAIT)
instruction before most of the 80287

The Intel 80287 was produced at speeds ranging
from 5 to 12 MHz. Other companies produced 16 MHz
and 20 MHz versions of the FPU.
AMD, Cyrix, and IIT also made 287's.