Programming Interface
The coprocessor extends the data types, registers, and instructions
to the microprocessor.
The coprocessor has eight 80-bit registers, which provide the
equivalent capacity of the 40 16-bit registers found in the
microprocessor. This register space allows constants
and
temporary results to be held in registers during calculations, thus
reducing memory access and improving speed as well as bus
availability. The register space can be used as a stack
or
as a
fixed register set. When used as a stack, only the top two stack
elements are operated on. The figure below shows
representations of large and small numbers in each data type.
Significant
Digits
(Decimal)
Data Type
Bits
(Decimal)
Approximate Range
Word
Integer
16
4
-32,768
~
X
~
+32,767
Short
Integer
32
9
-2x10
9
~
X
~
+2x10
9
Long
Integer
64
18
-9x10
18
~
X
~
+9x10
18
Packed Decimal 80
18
-9
..
99
~
X
~
+9
..
99
(18
digits)
Short
Real
.-
32
6-7
8.43x10-
37
~
I
XI
~
3.37x10
38
Long
Real
....
64
15-16
4.
19x
1
0-
307
~
IXI
~
1.67x10
308
Temporary Real 80
19
3.4x 1
0-
4932
~
IXI
~
1.
2x
10
4932
* The
Short
Real and
Long
Real
data
types
correspond
to
the
single
and
double
precision
data
types.
Data
Types
Hardware Interface
The coprocessor uses the same clock generator and system bus
interface components as the microprocessor. The
microprocessor's queue status lines
(QSO
and QS1) enable the
coprocessor to obtain and decode instructions simultaneously with
the microprocessor. The coprocessor's
'busy'
signal informs the
microprocessor
that
it
is
executing; the microprocessor's WAIT
2-4 Coprocessor
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