HP 3000 III Series Manual page 322

Interr upt System
8-27. PRIVILEGED MODE VIOLATION. This trap is caused by an
attempt to execute a privileged instruction in user mode (that
is, when bit 0 of the Status Register is 0). This violation also
occurs in EXIT if an attempt is made to exit from user to priv-
ileged mode or if exiting from user mode and the external inter-
rupts bit in the status word has been altered.
8-28. STACK OVERFLOW. A stack overflow results from attempting
to stack more data than can be contained on the current stack (SM
greater than Z). The system makes the decision whether to abort
the p roces s or to expand the s ta ck.
8-29. INTEGER OVERFLOW. An integer overflow occurs when the
result of an integer operation (ADD, SUB, etc.) is outside the
allowable range of integers which is -32768 to +32767.
8-30. FLOATING-POINT OVERFLOW. This trap occurs when the magni-
tude of the result of a two-word floating-point operation is lar-
ger than the largest representable floating-point number which is
1.157921
x
10
8-31. FLOATING-POINT UNDERFLOW. This trap occurs when the mag-
nitude of the result of a two-word floating-point operation is
less than the smallest representable positive number which is
8.63617 x 10 , and is not equal to zero.
-78
Note
Floating-point overflow and underflow can
best be understood by referring to the
chart below showing the range of valid
numbers.
x
10
77
if it is between A and B,C and D, or equal to
o.
I
A
where
A
=
-1.157921
B
=
-8.63617
C
=
8.63617
D
=
1.157921
A number is valid
I
B
x
10
77
x
10
x
10
o
I
C
I
D
8-16 .