Contrologix/Logix 5000

Hi
I have a few of questions:
1. I've created a 'program' underneath a 'task'. Why can't I delete this program. There are no routines or tags in the program.

2. If I 'alias' a tag, does this take up time/processing power.

3. I understand that BOOL tags take up 32 bits as a minimum. If I create BOOL tags as I need them does this just waste memory or are there other implications. I don't like the idea of accessing bits as tag[10] or tag[24]. I'd like each to be called something meaningful.

Thanks for your time

Paul

Don't you people sleep? Just because I don't is no reason for you to all take up the habit.

I happen to be up tonight writing a basic ladder logic PID lab, so I have a few answers for you.

1. When you create a Program underneath a Task, notice there is a field marked "Schedule in:" in the dialog box where you give the task a name.

If you click on the selector list arrow, you'll see that by default RSLogix 5000 is scheduling your new Program to execute in the Task you created it in, but you could also schedule it in a different Task, in <none>, or in the special tasks Controller Fault Handler or Power-Up Handler.

Right-click on the Task and select Properties, then Program Schedule. If you remove that new Program from the Task's schedule of programs to run, it shows up in the Controller Organizer as an Unscheduled Task. From there, you can delete it.

There are a set of rules for what can be deleted in RSLogix 5000 and I usually have to re-discover them every time I start gutting a program. I think tag databases must be empty, and routines must have no logic. But I'd have to check to be sure.

2. As I understand it, "Aliasing" a tag doesn't take up noticeable processing power. It's not like the controller has to do housekeeping and run a big series of internal MOV and COP commands. Aliases are like data pointers that are defined when the tag is defined, so they're part of the program when it is downloaded and compiled.

That's why you can't change an alias online, and why when you create a tag online you have to be sure to get to the Type or Alias fields before pressing Enter or the Tag will be created and can't be edited, only deleted and re-created.

I think there are some exceptions, such as large multidimensional file instructions, in which direct-referenced tags are faster than aliased ones. I'd have to look into that after a long nap.

3. This is kind of a "coffee vs. tea" question. It depends on what you like and what you want.

ControlLogix is a 32-bit system, and all tags with atomic datatypes take up 32 bits. If you create a BOOL, a SINT, and an INT, they take up the same amount of memory as three DINTs.

In fact, it's slightly slower to perform some instructions on BOOL, SINT, or INT datatypes than it is to perform them on native DINT datatypes. Again, I'd need a nap and a reference book to explain this in depth.

If you want your binary elements to have unique names and meanings, go ahead and use BOOL data types.

If you want to have a bunch of bits that are treated as sub-indices to an array like they are in the SLC or PLC-5, use BOOL[32] arrays.

And don't use a little thing like the Atlantic as your excuse. This is no time of the wee morning hours to be up fiddling with logic controllers.

thanks

Ken - thank you very much for your help.
Now go to bed

Hi. This is a bit hard to put to paper. From my understanding if you create a bool as the first tag, it takes 1 memory space. If you then create a dint it will leave the next 31 spaces empty and then use the next full double word space. Similarly if you create 7 Bools, 1 Sint and 1 Int then there is 1 space left. If you create anything over 1 space it will start again in the next double word space.
When I create tags, ( ie new project, not just a one off creation), my theory is that you create a DINT which means that you are at the start of a new double word boundary then create Bools in groups of 32, ints in multiples of 2 etc. This was the way it was all explained to me at an Rockwell integrators forum. If I search hrd enough I could find the docs to back this up if required. Regards Alan Case