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IBM 7090 User Manual

IBM 7090
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Clear
and Add
Logical
Word
CAL
-0500
(I,
E)
Figure
5.3-14
This
instruction
clears
the
AC(S,
Q,
P,
1-35)
and
enters
the
word
stored
at
the
location
indicated
by
the
address
into
AC
(P,
1-35).
This
instruction
operates
the
same
as
CLA
except
that
the
(S)
of
the
word
is
sent
to
AC(P).
The
sign
of
the
word
in
the
AC
is
positive.
Add
ADD +0400 (I,
E)
Figure
5.3-15
This
instruction
causes
the
word,
stored
at
the
location
indicated
by
the
address,
to
be
added
algebraically
to
the
contents
of
the
AC.
The
resulting
sum
or
difference
re-
places
the
AC
factor.
The
following
rules
of
addition
are
used
during
the
execution
of
the
add
instruction:
1.
Accumulator
and
storage
register
signs
alike:
a. Add
true
accumulator
factor
to
the
storage
register
factor.
b.
The
accumulator
sign
is
unchanged.
2.
Accumulator
and
storage
register
signs
unlike:
a. Add 1
's
complement
of
the
accumulator
factor
to
the
storage
register
factor.
(1)
If
no
end-carry
results,
complement
the
accumulator
factor
and
leave
the
accumulator
sign
unchanged.
(2)
If
an
end-carry
results,
add
one
to
the
result
and
change
the
accumulator
sign.
Except
for
bringing
a
word
from
storage
to
the
SR,
most
of
the
execution
of
this
instruction
is
accomplished
during
the
I
cycle
of
the
next
instruction.
The
contents
of
the
AC
or
the
l'
s
complement
of
the
AC
and
the
contents
of
the
SR
are
added
in
the
adders.
Whether
to
use
true
AC
or
complemented
AC
is
determined
by
the
comparison
between
the
AC
and
SR
signs.
Complement
addition
is
used
to
obtain
the
difference
be-
tween
the
contents
of
the
SR
and
the
contents
of
the
AC.
The
difference
between
the
SR
and
AC
contents
can
be
a
complement
number
or
a
true
number.
The
result
will
be
in
complement
form
if
the
AC
is
larger
than
the
SR
factor.
A
true
number
will
result
if
the
AC
factor
is
smaller
than
the
SR
factor.
Dur-
ing
the
addition
a
carry
out of AD
position
Q
indicates
that
the
AC
factor
is
smallerand
no Q
carry
indicates
that
the
AC
factor
is
larger.
To
remember
the
carry,
a Q
carry
trigger
is
turned
on
by
a
carry
out
of
AD
position
(Q).
If
the
result
of
the
complement
addition
is
a
true
number
it
is
one
less
than
it
should
be
because
the
1
's
complement
rather
than
the
2's
complement
was
used
in
the
addition.
Therefore,
a
one
is
added
to
the
result
in
the
AC
to
get
the
correct
difference.
If
the
result
of
the
addition
is
a
complement
number,
it
must
be
re-complemented
to
get
the
correct
true
number.
The
sign
of
the
result
in
the
AC
is
set
the
same
as
the
sign
of
the
largest
original
factor,
as
determined
by
the
status
of
the
Q
carry.
Example
1
Signs
Alike
-7
+
(-6)
=
-13
-0111
SR(7)
-0110
AC(6)
-1101
Result
in
AC
(13)
58

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IBM 7090 Specifications

General IconGeneral
CategoryMainframe Computer
Introduced1959
Transistor-basedYes
Word Length36 bits
Add Time4.8 microseconds
MemoryCore memory
Memory (words)32, 768 words