Question Time Again

Hello All,

Once again I have another question (surprise surprise). I've read quite a bit on these boards, posted a few times etc but I am wondering about indirect addressing. What are the advantages of it? Whats an good example of it?

I am trying to broaden my knowledge, so I guessed this would be a good thing to learn since it seems that it is used by various people on these boards.

Thanks,

Lionel

A good example is using an integer to offset another integer.


Lets say you need to store information by the hour. So many counts per hour, and keep each hour seperate. Create a file with at least 24 integers. We'll say N15:0-23 Then use the hour marker (S:40) to move data to the correct hour between N15:0 and N15:23 this is done by N15:[S:40] Brackets indicate an indirect address. The result is that the value of S:40 will offset the integer that the data is moved to.

Each hour S:40 incresses and it starts at 0 for the hour between Midnight and 1:00 am. So for the first hour you will move X counts into N15:0. S:40 is 1 for the hour between 1:00am and 2:00am, so for that hour you would move the counts into N15:1, and so on. It starts over at midnight. So remember that the information will overwrite the preceeding day. Different problem, different day.

These are AB addresses. They may or may not be what you are use to seeing.

Hope this helps.

Okay I understand it now, and yes AB is what I am use to.

I just never fully grasped the concept behind it.

One caution on indirect addressing - it can be difficult to follow the logic. Make sure you take extra pains in commenting so that it is clear exactly what is going on.

I think that is what has caused the most confusion for me. I have been reviewing some ControlLogix Programs that heavily uses InDirect addressing and I can't really figure out what it is doing. Very little comments in it.

I've been sticking with the other programs that has good clear comments that I can learn from.