s15 bit

I have seen a normally open bit addressed s15 usually the first bit in the first rung that has the description "first Pass". I attended a rockwell seminar in micro PLCs and one of the exercises had this bit in it related to a high speed counter. I did not have a chance to ask the instructor what this address is. I have a PLC book that has an example of this but does not say where this address comes from or the description of "first pass". Thanks in advance.

Herb

This is a bit in the Status data file that is only true during the first execution ("scan") of the logic program. This can be the first scan after powerup, or the first scan after a Program -> Run mode transition.

The actual address is S2:1/15. Most users abbreviate this as S:1/15 because there's only one "S"-type data file in PLC-5/SLC500.

In ControlLogix, the same function is served by the S:FS boolean tag.

Here's the best list I've found for what all those status files are and how they work. I mean, I've only actually used like 4 of them in a program ... but the rest of it looks pretty impressive too.

Bah, once again technology kicks my butt. Tried to attach the file but it was too large. Its Appendix B in the SLC instruction set manual. Publication 1747-RM001C-EN-P-September2001 in case anyone wants to look it up.


-jeff

Try this....