Chapter 17 IBM 650 instruction logic 221

contents of the upper half of the accumulator. The contents of the lower half of the accumulator will remain unaffected unless the subtraction causes a change of sign in the accumulator, in which case the contents of the lower half of the accumulator will be complemented. Also, the units position of the upper half of the accumulator will be reduced by one.

16 SL (Subtract from Lower). This operation code causes the contents of the D address location to be subtracted from the contents of the lower half of the accumulator. The contents of the upper half of the accumulator could be affected by carries.

60 RAU (Reset and Add into Upper). This operation code resets the entire accumulator to plus zero and adds the contents of the D address location into the upper half of the accumulator.

65 RAL (Reset and Add into Lower). This operation code resets the entire accumulator to plus zero and adds the contents of the D address location into the lower half of the accumulator.

61 RSU (Reset and Subtract into Upper). This operation code resets the entire accumulator to plus zero and subtracts the contents of the D address location into the upper half of the accumulator.

66 RSL (Reset and Subtract into Lower). This operation code resets the entire accumulator to plus zero and subtracts the contents of the D address location into the lower half of the accumulator.

20 STL (Store Lower in Memory). This operation code causes the contents of the lower half of the accumulator with the accumulator sign to be stored in the location specified by the D address of the instruction. The contents of the lower half of the accumulator remain undisturbed.

It is important to remember that the D address for all store instructions must be 0000-1999. An 8000 series D address will not be accepted as valid by the machine on any of the store instructions.

21 STU (Store Upper in Memory). This operation code causes the contents of the upper half of the accumulator with the accumulator sign to be stored in the location specified by the D address of the instruction. If STU is performed after a division operation, and before another division, multiplication, or reset operation takes place, the contents of the upper accumulator will be stored with the sign of the remainder from the divide operation (Op-Code 14). The contents of the upper half of the accumulator remain undisturbed.

22 STDA (Store Lower Data Address). This operation code causes positions 8-5 of the distributor to be replaced by the contents of the corresponding positions of the lower half of the accumulator. The modified word in the distributor with the sign of the distributor is then stored in the location specified by the D address of the instruction.

23 STIA (Store Lower Instruction Address). This operation code causes positions 4-1 of the distributor to be replaced by the contents of the corresponding positions of the lower half of the accumulator. The modified word in the distributor with the sign of the distributor is then stored in the location specified by the D address of the instruction. The contents of the lower half of the accumulator remain unchanged, and the sign of the accumulator is not transferred to the distributor. The modified word remains in the distributor upon completion of the operation.

17 AABL (Add Absolute to Lower). This operation code causes the contents of the D address location to be added to the contents of the lower half of the accumulator as a positive factor regardless of the actual sign. When the operation is completed, the distributor will contain the D address factor with its actual sign.

67 RAABL (Reset and Add Absolute into Lower). This operation code resets the entire accumulator to zeros and adds the contents of the D address location into the lower half of the accumulator as a positive factor regardless of its actual sign. When the operation is completed, the distributor will contain the D address factor with its actual sign.

18 SABL (Subtract Absolute from Lower). This operation code causes the contents of the D address location to be subtracted from the contents of the lower half of the accumulator as a positive factor regardless of the actual sign. When the operation is completed, the distributor will contain the D address factor with its actual sign.

68 RSABL (Reset and Subtract Absolute into Lower). This operation code resets the entire accumulator to plus zero and subtracts the contents of the D address location into the lower half of the accumulator as a positive factor, regardless of the actual sign. When the operation is completed, the distributor will contain the D address factor with its actual sign.

19 MULT (Multiply). This operation code causes the ma chine to multiply. A 10-digit multiplicand may be multiplied by