ONS and ORS instruction in Micrologix 1200 PLC (AB)


Thread Starter


I met a problem by using OSR instruction in Micrologix 1200 PLC. I'm very sure that I use it corretly, because in some programs, it works fine. But sometimes, OSR can't work, and I need to change it to ONS to make program work.

Do you guys have this problem before? Is there any difference between ONS and ORS?
Thank you!
So far I know, both instructions operate the same, just that one of them is available only for the micrologix 1000 and 1200/1500, the OSR instruction and there, in tne micrologix 1000 it operates as a intermedaite instruction before an output coil, while in the micrologix 1200/1500 it operates as an output instruction. In this one you have an output box with two variables to fill in, a storage bit and an output bit. The output bit becomes set (1) when all the previous conditions in the rung go from false to true and remains set just during one scanning cycle of the CPU, thereafter it is reset again. The storage bit is set during the transition from false to true of the previous conditions but remains set after the next scan cycles and it will be reset when the rung becomes false.
Be careful not to generate another output in the program with the same bit direction.