Subtract Word
(SR)
(S)
General Description
Format
(RRl
(RX)
Condition Code
Interrupt
Action
Fixed-Point
Insflructions
• The operand specified by
the
second address
(R
2
or
X~B2/D2)
is sub-
tracted
from
the
operand specified by
the
first address
(R
1
)
and
the
difference is placed in
the
general
register
specified by
the
first address
(R
1
).
The magnitude
and
the
sign of
the
difference determine
the
condition
code setting.
I
(SR)
1B
~ ~
0
7 8
11 12 15
I
(S)
5B
Rl
x
2
0
7 8
11 12 15 16
• 0 - difference is zero.
1-
difference
is
less
than
zero.
2 - difference is
greater
than
zero.
3 - overflow.
• Fixed-point overflow.
Address
error:
Addressing
(RX
format).
Specification
(RX
format).
B2
D2
19
20
31
Notes • 1. The operation is accomplished by adding
the
one's complement
of
the
second operand
and
a one
in
the
low-order position
of
the
first
operand. The one's complement
of
a
number
is
obtained by changing
all
the
1
bits
to 0
bits
and
all
the
0
bits
to 1 bits. All 32 bits
are
involved
in
the
operation. An overflow exists
if
the
high-order
numeric
result
bit
and
the
carry
out
of
the
sign
bit
position disagree.
2. The difference between a maximum negative
number
and
another
maximum negative number is zero
with
no overflow.
3. When
the
same
register
is specified
for
Rl
and
R
2
,
the
operation is
equivalent to clearing Rl
to
zero.
4. The operand specified by
the
second address is unaltered.
137
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