Ffl-ffu

roxusa

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Nov 2008
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A couple of questions with RS500 FFL-FFU instruction set.
1-Does the stack load from the bottom or the top, My stack is
#N7:50 with a length of 20, so does the first one go into 50 or 79.
2- Can I change a value in the stack with a move to that location.

I want to set up an HMI to view the stack and possibly make a change
to one of the words if needed. Thanks
 
Yeah, the FFL will load into N7:50 first and shift them down to N7:69

You can move integers to the direct addresses, always a good practice to document that in the logic so the next guy knows that the values in the stack may be altered from the hmi
 
A couple of questions with RS500 FFL-FFU instruction set.
1-Does the stack load from the bottom or the top, My stack is
#N7:50 with a length of 20, so does the first one go into 50 or 79.
2- Can I change a value in the stack with a move to that location.

I want to set up an HMI to view the stack and possibly make a change
to one of the words if needed. Thanks

The Logix 5000 FIFO (i.e., queue) works backwards. FFL inserts at the end and shifts toward the front (lower address). Is this a change from the RS500 behavior?
 
as the stack is emptied are the addresses in the stack returned to 0
 
Your best bet is to drop an FFL and FFU instruction onto a rung, click on it and press F1. The help file is quite detailed and includes some really nice graphics to show exactly how the instructions executes, and how and where the data moves to and from.
 
I have read the instruction set help for both the FFL & FFU but it doesn't mention which way it loads. I used it years ago on a conveyor system to send an integer with each load so the take off knows which way to discharge the load. I am doing another similar one and wanted to display load directions on the HMI.
I did figure out from reading the Help that the position is the next available open slot in the stack and it looks like since I am using R6:0 as my control register that would be R6:0.POS, I created a rung to subtract 1 from that and store in N7:0 to display the number of loads in stack at my discharge conveyor and will test to see if I'm correct
Thanks All for the input
 

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