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

vow wow. •1•01111111111111111■1111111“1•11111111111•1111111■11 111■1111.11•11111iARITHMETIC INSTRUCTIONSSix instructions are provided to perform addition, subtraction, or complementing ofdata residing in storage and/or the index register or accumulator.Add (PA)0 5 8 15Op code1 0 0 0 0III)RXXXI IDisplacement8 0-7 X XThe contents of the accumulator are added algebraically to the contents of the storagelocation specified by the effective address. The resulting sum replaces the contents ofthe accumulator; the contents of the addressed storage location are not changed.If R=000, the effective address of the data in storage is formed by using the IARas the base register. If the R field is nonzero (R=001 to 111), the effective addressis formed using an index register as the base register.The carry and result indicators are set to reflect the result in the accumulator.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 an add instruction. If an overflow occurs, the accumulator willcontain the correct low-order 16 bits of the result and the carry indicator will beturned on if the result is negative.The result of the addition is either positive or negative, depending upon themagnitude of the values used and whether the signs of the two operands are the same,as shown below.+ added to a + = +—added to a — =+ added to a — = sign of the larger operand—added to a + = sign of the larger operandThe value in the accumulator is positive if the leftmost bit is a 0; the value in theaccumulator is negative if the leftmost bit is a 1. Negative numbers are intwos-complement form.Example:0 5 8 15PA instruction(R = 110 specifies using XR6to generate the EA)Op code1 0 0 0 0III!1 1 0IDisplacement0 1 0 10 10 08 6 5 2Contents of accumulator 0000 0000 1001 1101Contents of storage locationaddressed by PA instruction + 0000 0010 0011 0101Result in accumulator 0000 0010 1101 00104-14 GA34-0003