If a continuation of the one-shot output is not needed beyond the current rung then the ONS is the more obvious choice. The OSR instruction is just a box and, except for the name, doesn't give as visually obvious clue as to its effect - the second bit of this instruction will be true only on the rising edge of the logic into this box. The part of the rung after this instruction will be true only on the rising edge of the logic before this instruction. The ONS instruction is the more intuitive to me. I'm thinking that the presence of two instructions with virtually the same effect comes from the various previous type processors (the PLC2/5 family and the SLC/Micrologix family) and the ways they provided this function. Just remember the effect of each instruction. It's really just a matter of programming preference.
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