RCA 70/46 Reference Manual page 146

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.
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