At
power-up the
BIOS
detects
the
80287 and enables hardware
interrupt 13.
The
interrupt handler clears
the
latched
BUSY
signal,
and transfers control
to
the
NMI handler. The NMI handler should
read the status
of
the coprocessor
to
determine
if
the
NMI was
caused by the 80287. If
it
was not, control should be passed
to
the
original NMI interrupt handler.
Capability Extensions
By
programming
with
the instruction set
of
the
80287
coprocessor the data types, registers, and instructions
to
the
microprocessor
are
extended. The data types are expanded
because the 80287 deals
with
these directly rather than
employing a program sub-routine. The register space
of
the
coprocessor
is
equivalent
to
the register space
of
the
microprocessor, but it
is
organized
as
eight 80-bit registers. This
register space allows constants and temporary results
to
be held
in
registers during calculations, thus reducing memory
accesses
and
improving speed
as
well
as
system bus availability. The register
space can
be
used
as
a stack
or
as
a fixed register set. When used
as
a stack, operations are only on
the
top
two
stack elements.
Numeric Coprocessor
101
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