Hardware Interface - IBM AT 5170 Technical Reference

The following figure shows representations of large and small
numbers in each data type.
Significant
Digits
Data Type Bits (Decimal) Approximate Range (Decimal)
Word Integer 16 4
-32,768
~
x
~
+32,767
Short Integer
32
9
-2x10 9
~
x
~
+2xl0 9
Long Integer 64 19
-9x 1 0 18
$
x
~
+9x 1 0 18
Packed Decimal 80 18 -9 .. 99
~
x
$
+9 .. 99 (18 digits)
Short Real
I<
32 6-7
8.43xl0· 37
~
x
~
3.37xl0 38
Long Real
I<
64 15-16
4. 19x 10- 307
~
x
~
1.67xl0 308
Temporary Real 80
19
3 . 4x 10- 4932
~
x
~
1.2xl0 4932
Data Types
*
The Short Real and Long Real data types correspond to the
single and double precision data types.
Hardware Interface
The coprocessor uses the same clock generator as the
microprocessor. It works at one-third the frequency of the system
microprocessor (2.66 MHz). The coprocessor is wired so that it
functions as an I/O device through I/O port addresses hex OOF8,
OOF A, and OOFC. The microprocessor sends OP codes and
operands through these I/O ports. The microprocessor also
receives and stores results through the same I/O ports. The
coprocessor's
I
busy
I
signal informs the microprocessor that it is
executing; the microprocessor's Wait instruction forces the
microprocessor to wait until the coprocessor is finished executing.
The coprocessor detects six different exception conditions that
can occur during instruction execution.
If
the appropriate
exception mask within the coprocessor is not set, the coprocessor
sets its error signal. This error signal generates a hardware
interrupt (interrupt 13) and causes the
I
busy
I
signal to the
coprocessor to be held in the busy state. The
I
busy
I
signal may
2-4 Coprocessor