Logix5000 FIFO manipulation

As mentioned earlier, I use UDT (1 string + 1 bool) for the FIFO.
The are set\reset from the HMI. Any suggestion on how to setup in plc such that only one bool out of the array can be set at the time? I.e. if one bool already set - disallow setting another, or reset the previous one and set the next.
The trouble I'm facing is that with the FFL and FFU instructions those bools are shifting as well (as I want them to), but I want to ensure only one is set at the time.

I am assuming that you are only adding to the array is with the FFL
If that’s the case then before you trigger the Load do a file search on the array and set a bool to true if any of the array elements are true
Then either don’t load the FIFO ir just set the bool in load tag to false
I would need more details on your application to full understand what you need

GaryS said:

I am assuming that you are only adding to the array is with the FFL
If that’s the case then before you trigger the Load do a file search on the array and set a bool to true if any of the array elements are true
Then either don’t load the FIFO ir just set the bool in load tag to false
I would need more details on your application to full understand what you need

Click to expand...

Correct me if I'm wrong, but FSC instruction doesn't work with BOOL arrays

I wouldn't use an FSC for this anyway to much overhead
set test tag to 0
set a simple loop for x = 0 to max array size
if array[x] = 1 set test tag to 1
x = x +1
loop

GaryS said:

I wouldn't use an FSC for this anyway to much overhead
set test tag to 0
set a simple loop for x = 0 to max array size
if array[x] = 1 set test tag to 1
x = x +1
loop

Click to expand...

A little more details on my setup.
UDT[100] (1string, 1bool) goes through FIFO - FFL and FFU. The data is stored in the string of the UDT. I use the bools to mark the string for removal or insertion (see above posts for details). This bool is (re)set on the HMI button for each UDT[x]. I want to ensure that pressing one button (setting one of the UDT[X].bool) resets all of the others.

Using your suggested method will indirectly cause the for loop to run every FFL and FFU. I just want to have one UDT[X].bool set, when done so through HMI. But I want to have the function native to PLC. In case someone does testing in the future without HMI.

May not be the most elegant solution, but solved with:

1. get UDT[] FIFO size: FIFO_size

• get last POS of FIFO: FIFO_size -1 = Last_POS

• if none of the bools are selected: (all of the UDT[x].bool xic's ANDed)
  FIFO_Select_POS = FIFO_size

• else:
  move the number associated with the set bool to FIFO_Select_POS

• clear all bools

• if 0<FIFO_Select_POS<Last_POS, set udt[FIFO_Select_POS].bool

The idea, if none of the bools are set POS=FIFO_size, else POS = the number associated with the bool position in the UDT[]. And obviously all of my functions before accessing the UDT[FIFO_Select_POS] make sure that 0<FIFO_Select_POS<Last_POS