one shot

In the one shot tutorial you use one monetary switch to control one output.I understand the interlock section(rung 2),but where does the output 1001 come from?Is this an internal instruction and if so is addressed using the one shot bits?

thanks
cdmac

I think the coil you are talking about is an internal "flag" or "coil". It is used internal only. The address will depend on the plc brand.

Here's a link, so everyone can play along.
http://www.plcs.net/chapters/oneshot18.htm

The bits in question can be anything, but perhaps it's best to think of address 0000 as being driven by a Pushbutton, and address 1001 is an internal address which drives an output for Pilot light at 0500.

The upshot of the logic is that, when you push the pushbutton, address 1000 is ON only for one scan. But that causes the state of the light to toggle ON on the first push, OFF on the second push, ON on the third push, and so on.

Phil could perhaps have used 0500 everywhere instead of 1001, but not all brands of PLC allow you to reference output addresses in contacts (I don't think they make those kinds of PLCs anymore, but I think I remember hearing about them). Plus, it's a little easier to follow the code if you aren't worrying about whether the light is ON or not while you're evaluating the bits.

I wouldn't call rung 2 "interlock" logic - it's a classic toggle, probably the most commonly used. "Interlocking" is where you prevent an output from comming on unless some (safety) condition is met.

Thanks

Thanks for the info.It makes a little more sense to me adressing the output 0500 in the flipflop circuit than the 1001 used.Again thanks alot.

cdmac