RsLogix 500 - Data Table Configuration and Sizing
In the previous lesson, RsLogix 500 - Analog Scaling, you ran into a problem with step 7 trying to add a rung address F8:1. We instructed you to go offline, make the change, download it, and then go back online but didn't give you much explanation.
Open up the program that you ended up with at the end of the RsLogix 500 - Analog Scaling lesson so you can dig into this further.
1. In the left pane, open up the F8 - FLOAT data table. Notice that there are only two data points. F8:0 and F8:1.
2. Using online edits, change the F8:0 to F8:2, then try to accept it. When you do, you get a prompt saying "Rung Has Errors. Cannot Accept!". Additionally, there are details at the bottom of RsLogix 500 circled below saying "Unable to create data table". It also gives you the specific location, rung 0 instruction 1.
3. The reason for this is that the data table you viewed in step 1 cannot be expanded without redownloading the program. So you understand what happens when you do this offline, cancel the edit, go offline, make the same edit you did in step 2 but do not download the program. Open the F8 - FLOAT data table in the left pane again. Still, there is only two addresses available, F8:0 and F8:1.
4. Click the "Verify Project" icon then click back on the F8 - FLOAT data table. Notice now there is a F8:2 data point. This wasn't magic. Clicking the Verify Project button checks that the data tables are of appropriate size and expands them if necessary.
5. These data tables can be expanded before it is necessary by clicking on the Properties button and changing the number of "Elements" up to a maximum of 256. Go ahead and change the element number to 256 and click OK.
6. Now you can see F8:0 through F8:255.
7. Beside the property button is the "Usage" button. Click it. This shows you what data points are being used in you program represented by an "X".
8. You can view all of the data file sizes by right clicking the "Data Files" in the left pane and selecting Properties.
9. The "Elems" column tells you how many of each data type you have. The OUTPUT, INPUT, and STATUS data files are fixed but the rest can be expanded.
10. One more important thing before you close this. So far you have worked with the B3 Binary, T4 Timer, C5 Counter, N7 Integer, and F8 Float data types because they are the defaults. Other data files can be created with with these data types as well. Click the "Create New" button. It will default to the next available file number, in this case 9. Then you can select from a variety of data types. Notice we left out the R6 Control data file but you will learn about it in a later lesson.
11. The next big question we always get is "what size should you put the data file at?". Again, we don't like to make rules but especially on PLC programs that we know that we will have to make online edits to, we usually expand all the data tables to their maximum size.
Another key advantages of using multiple data files is that it can help you keep your information organized. So for example by default your PLC has the N7 data file, but you could also create an N10, 15, and N21 (random numbers used) if it helps you organize your data better.
Continue on to the RsLogix 500 - Data Types B3 T4 C5 R6 N7 F8, What do They Mean lesson where you will learn more about each data type.