IBM System/7 Functional Characteristics - All about the IBM 1130 ...

NMI INNI 1111=111111 IM11111■111111111111 III II II IIIThe carry indicator is set on if a borrow occurs out of the high-order bit in theaccumulator.The overflow indicator is set to reflect the result only if it has not been set bya previous operation. If the overflow indicator was previously set on, it will not bechanged by the result of a subtract instruction. If an overflow occurs, the accumulatorwill contain the correct low-order 16 bits of the result and the carry indicator willbe turned on if the result is negative.The result indicators are set to reflect the result in the accumulator.The sign of the result is dependent upon the signs and magnitudes of both operands.Possible combinations (where operand B is always numerically greater than operand A,regardless of signs) are:From Operand Subtract Operandin Accumulator in Storage+B +A+B —A—B +A—B —A+A +B+A —B—A +B—A —BSign of Resultin AccumulatorThe value in the accumulator is positive if the leftmost bit is a 0; the value inthe accumulator is negative if the leftmost bit is a 1. Negative numbers are intwos-complement form.Example 1:Contents of accumulator 0 000 0000 0000 0011Contents of storage locationaddressed by PS instruction —0 000 0000 0000 0010Result in accumulator 0 000 0000 0000 0001(In decimal: 3 — 2 = 1)Example 2:Contents of accumulator 1 000 0000 0000 0011Contents of storage locationaddressed by PS instruction —0 000 0000 0000 0010Result in accumulator 1 000 0000 0000 0001(In decimal: —32,765 — 2 = —32,767)Example 3:Contents of accumulator 1 000 0000 0000 0011Contents of storage locationaddressed by PS instruction —1 000 0000 0000 0000Result in accumulator 0 000 0000 0000 0011(In decimal: —32,765 — (-132,768 = —32,765 + 32,768 = +3)+