s7 question

L 80
T DIW 196
SET
S DIX 198.0
NOP 0

with the above code the load and transfer function is straight forward and the " S DIX 198.0" sets bit zero in byte 198 but what does the term" SET" actually do ive looked in the book and it refers to setting the "RLO" but i still dont understand what this function is doing there.
what would happen to this logic if the word "set" was not there.
thanks in advance

Hello darren.s;

In the short example you give, SET has no consequences. But if in the next few lines you have RLO-dependent logic, such as =M2.1 or JC M001 or JCN M001, then having set the RLO to 1 would have an impact.
Maybe you could post the whole rung so we could examine it.

Hope this helps,
Daniel Chartier

The "S DBX198.0" function only works if the RLO is on. RLO = "Result of Logic Operation". So the code in front of the "S" determines if the bit will be set. The SET instruction sets the RLO. Therefor the bit DBX198.0 will be set to 1, recardsless of any logic before the sets. I know programmers that always use the SET instruction before any bit S/R commands. This way the don't have to think about RLO's. I had it once that a bit was not set evethough I used the "S" instruction. The machine was not responding in a way I would have expected. Nowadays I only use the SET instruction if the logic in front is complex and the bits are very powerfull. (In a robot program enable move diagonal for instance)

Thanks for making that clear, Werner. I had forrgotten that S and R instructions were RLO dependant.

Daniel Chartier

thanks for your help guys