Clearing Large Data Structure

awaege

Member
A
Join Date
Jun 2019
Location
Appleton WI
Posts
10
I am currently working in RSLogix 5000. I have a large data structure with the following general structure:

UDT[0]
Dataset1​
Min​
Max​
Avg​
Data[90]​
Dataset2​
Min​
Max​
Avg​
Data[90]​
Dataset3​
... etc
UDT[1]
.... etc


Total there are 22 data-sets with the same structure and two UDT instances. One to store incoming data and one to analyze the previous data and store it.

After the data in UDT[0] is passed to UDT[1] I need to completely clear UDT[0] to prevent any lingering data to interfere with the calculations since the Data[90] may not always be completely filled.

I've been debating the best way to go about this. Using FLL instructions seems like it might work but with the current structure I would need many FLL insturctions to do the job.

Does anyone have any advice on how this might be most efficiently accomplished?
 
To pass for UDT[0] to UDT[1] I just use a COP instruction. My hope was to avoid using a blank UDT since this would create a third instance of an already massive structure in an application where I am very tight on memory. That is my backup plan though.
 
If dataset was an array you could create a logic loop with a pointer and loop thru all 22 indexes inside udt[0] to clear with three CLR and 1 FLL using indirect addressing.
If dataset isn't an option to be an array then nevermind ��
 
90 elements is not massive. If you are really so tight that 90 elements makes a difference you might need to re-evaluate the hardware. A loop or FFL is the only other way.
 
Unless you turn your dataset into an array of dataset[22] you can't do didly about iterating it without brute forcing the dataset1, dataset2 etc.
 
Create a new Instance of the Array and set up your new initialization values (0 if that's what you want) then make it constant.

Otherwise you have COP or FLL instructions.


Regards

Daniel.
 
TheWaterboy said:
90 elements is not massive. If you are really so tight that 90 elements makes a difference you might need to re-evaluate the hardware. A loop or FFL is the only other way.
Click to expand...

No 90 elements is not massive. However the entire structure contains about 500 instances of [90] arrays of 32 bit reals and there are currently three instances of the structure making my current memory use at approximately 500,000 bytes or about 25% of a 1769-L33ER CompactLogix 5370's capacity which is what this will be running on.
 
awaege said:
...in an application where I am very tight on memory. That is my backup plan though.
Click to expand...

awaege said:
...my current memory use at approximately 500,000 bytes or about 25% of a 1769-L33ER CompactLogix 5370's capacity which is what this will be running on.
Click to expand...

I'm not following, you have plenty of memory, where else are you eating memory? Complex data structures will consume the bulk of a processor's memory. The actual programming logic won't have nearly the impact.

You've hit an area of compromise due to the data structure that is in place. As others have said simply using a COP to copy and empty UDT into the destination UDT is the easiest logic solution. But if you are concerned about memory, then alternating your programming approach is required.

I would consider creating a blank instance of a single dataset structure to minimize the overall hit on memory, then brute force the clearing

Code: 
// EmptyDataset as UDT[#].Dataset structure


UDT[0].Dataset1 := EmptyDataset
UDT[0].Dataset2 := EmptyDataset
UDT[0].Dataset3 := EmptyDataset
.
.
.
UDT[0].Dataset22 := EmptyDataset
 
Paully's5.0 said:
I'm not following, you have plenty of memory, where else are you eating memory? Complex data structures will consume the bulk of a processor's memory. The actual programming logic won't have nearly the impact.
Click to expand...

The issue here is that this is being done on a controller that already has about 65-70% of memory used. I argued that it would make much more sense to push everything into a SQL database and not do large data collection and analysis inside a PLC! But the powers that be can't seem to understand that and I am forced to go this route. (n)

I will probably just go with the brute force approach. I don't think anything else is going to work here. Thanks for the input.
 
Another consideration, change the UDT[#].Dataset to an array as well.

UDT[#].Dataset[#] rather than the Dataset1, Dataset2. Gives you more options such as iteration or FLL on UDT[0].Dataset[0]
 
awaege said:
Yes I am going to do that as well. Makes much more sense in retrospect.
Click to expand...

One more tag of the UDT set to all zeroes (constant tag so it can't be changed), I don't think is going to break the bank.

Then COP it to the UDT you want to clear. Better still, use CPS.
 
Last edited:
Can be done in one instruction:
FLL 0 UDT[0] 1 will clear whole UDT[0]
FLL 0 UDT[0] 5 will clear UDT[0] to UDT[4] - all in one instruction
COP UDT[1] UDT[2] will copy all members of UDT[1] to UDT[2]
 

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