SIMATIC Statement List for S7-300 and S7-400

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+I(add 16-bit integer numbers) adds the contents of ACCU 1-L to the contents of ACCU 2-L and stores the result in ACCU 1-L. The contents of ACCU 1-L and ACCU 2-L are interpreted as 16-bit integer numbers. The instruction is executed without regard to, and without affecting, the RLO. The status word bits CC 1, CC 0, OS, and OV are set as a function of the result of the instruction. The instruction produces a 16-bit integer number instead of an 32-bit integer number in the event of an overflow/underflow.
The contents of accumulator 2 remain unchanged for CPUs with two ACCUs.
The contents of accumulator 3 are copied into accumulator 2, and the contents of accumulator 4 are copied into accumulator 3 for CPUs with four ACCUs. The contents of accumulator 4 remain
unchanged.