Incrementing Words

i'm using RSlogix 500 and have a bunch of floats that i'm trying to store data in. For example, every incrementing 100 pounds of pressure i am measuring the weight on some material caused by that amount of pressure. after taking and storing the first data value in my first float, i want to go to 200 psi and measure and store that value in float 2. Is there a way in ladder logic to do this looping method while changing the storage float (F8:1, F8:2, F8:3...)

hgtwn,

I suggest that you use the method called "Indirect Addressing". This is pretty simple to use, and you can get all the information you need from the RSLogix Help files. Click "Help", "SLC Instruction Help", then from the command list, click on any command that can implement indirect addressing, for example the "MOV" command. You will see directions on how to use that command with indirect addressing.

Basically, indirect addressing tells the command: do not get your number from this location, but instead go to this memory location and use the number found there as a pointer and then go to the memory loaction indicated by the pointer. You can see then that it is just a matter to increment the pointer each iteration through your loop.

Another method that could be used, but is less flexible, is to use the FFL and FFU commands. These work best if the number of data points is fixed, always the same number of 100 pound increments to read in, which in your case it might be. FFL, when triggered, loads data from a memory location into a series of words. FFU is used to "Unload" the data, with the order being "first in, first out".

i've been looking all over the help for examples and i just don't really understand this, especially the use of # before my address. Is there a possibility that i could get an example here? say, i have an input I:2.1 and which reads my weight. the pressure is changing so the weight is changing also, so every 20 seconds i want to take the value in I:2.1 and put it into a floating word. The first reading goes in F8:1 all the way to the last reading which goes in F8:45.

hgtwn said:

i've been looking all over the help for examples and i just don't really understand this, especially the use of # before my address. .

Click to expand...

The # sign is used with indexed addressing, I agree with Lancie 1, indirect addressing would be best for your application, and I find it is easier for the less experienced to follow.

If I read it right, you're looking for 900 seconds of history at 20 second intervals, is this correct?

yeah thats right, 900 seconds of history time. is it even possible to use floats in SQO? How would i go about using indirect addressing? can i use floats with that?

Here's a pdf file to get you started.

thanks! i'm heading home. i'll take a look at it there and hopefully i'll be on my way! thanks again

Ken,
That was a very well-written example. Even I could see how it works. Good job!