INTERRUPT
ACTION
Address
Error
Floating-Point Instructions
• The following
interrupt
conditions can occur as a result of a floating-
point instruction.
Addressing • An address
error
interrupt
occurs when an address in the RX instruc-
tion
format
specifies a location outside the available main memory. The
operation is terminated
at
the point of error. The result
data
and
the
condition code
(if
affected)
are
unpredictable.
Specification • An address
error
interrupt
occurs
if
a
short
operand is not located on
a word boundary
or
a long operand is not located on a double-word boundary.
An address
error
interrupt
also occurs
if
a floating-point
register
other
than
0,
2,
4
or
6 is specified. The instruction is suppressed. The condition
code, the
data
in main memory, and
the
registers remain unchanged.
Address restrictions
do
not apply to the X
2
,
B2
and
D2
components
of
the instruction.
Protection • An address
error
interrupt
occurs when the protection key
and
the
storage key of the result location do
not
match. The operation is suppressed.
The condition code, the
data
in main memory,
and
the registers remain
unchanged. (This
interrupt
can only occur
if
the
memory protect
feature
is installed.)
Signiflcance
Error
• A significance
error
interrupt
occurs when the result
mantissa
of
an
add
or
subtract
operation is zero. A
program
interrupt
occurs
if
the
significance
error
mask
bit
in the
Interrupt
Mask Register of the
current
state
is set to 1. The operation is completed,
the
exponent is unaltered,
and
the
interrupt
is taken.
If
the significance
error
mask
bit
is zero,
the
interrupt
is prohibited and
the
operation is completed by
setting
the
result
to
true
zero (zero sign, zero exponent, and zero
mantissa).
In
either
case,
the condition code is
set
to zero.
Divide
Error
• A divide
error
interrupt
occurs
if
division by zero is attempted.
Exponent Overflow • An exponent overflow
interrupt
occurs when the result exponent over-
flows and the mantissa is
not
zero. The operation is terminated
and
the
result
data
is unpredictable. Addition and subtraction
set
the
condition
code to 3. Multiplication and division
do
not affect
the
condition code setting.
Exponent Underflow • An exponent underflow
interrupt
occurs when
the
result exponent is
less
than
zero and
the
result mantissa is not zero. The operation is com-
pleted by setting the result to
true
zero (zero sign, zero exponent,
and
zero
mantissa).
Addition and subtraction
set
the condition code to zero.
Multiplication and division
do
not affect
the
condition code setting.
204
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