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form
60
....
099,
which is
the
smallest
positive
quan-
tity
that
can
be represented
(Figure
33).
A zero
mantissa causes
the
E/Z
indicator (12)
to be turned
on.
Zeros
entered as
data
should
be in floating-point
zero
form. Zero
quantities
in other forms
, e.g.,
60
...
.
060
will
be
processed,
but results
cannot
be
assured.
Cor. Storage
lo
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Core Storoge
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ocol ions
01590_01599
Instruct ion
0159 0 - - 01599
Before
Afte
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Epi
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Eq
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P
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Q
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Figure 33.
Zero
Mantissa
Indicators
The four indicators
associated with
automatic floating-
point
operations are
represented by lights on the 1620
console.
The light for
each
indicator is turned on
when
the
corresponding
indicator
is
turned on. The
H/P
and
E/
Z
lights
are
located
in
the Control Gates
section
of the
console,
and
the Arithmetic Check and Expon-
ent
Check lights and Overflow
switch
are
in
the Indi-
cator
Displays
and
Switches section
(Figure
34
).
High/
Positive
(11 ).
The
H/P
indicator
and
light
are
turned on
when
the mantissa resulting
from a
floating-point
computation
is
greater
than
zero.
Equal/Zero
(12).
The
E/Z
indicator
and
light are
turned
on
to indicate a zero mantissa resulting from
a
floating-point
computation.
Arithmetic Check
(14).
During floating-point opera-
tions,
the Arithmetic Check indicator is turned on
when
division is
attempted
by zero. Division by
an
unnormalized number
may
result
in
an
incorrect quo-
tient through incorrect positioning of the divisor.
Exponent
Check (15). The exponent Check
indica-
tor is turned on by
exponent
overflow or underflow.
Exponent Overflow
When an exponent greater
than
+99
is
generated,
the
mantissa is set
to
nines.
The
sign
is determined by
the
computed
result that
caused
the overflow. The
exponent
is
set
to
+
99. This is the largest floating-
point number
(99 .
.
.. 999) that
can
be
represented.
If the
generated
mantissa is positive, the
H/P
indi-
cator (11)
is
also
turned on.
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SWIl(H[~
'w,
• •
•
• •
I
I
w'"
_~O«
10
CHIC
D"
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.,
• •
• • •
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ON
OH
Figure
34.
Indicators
and
Switches
on
1620 Console
28
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