Rslogix 500 FFL to Unity Pro.

So once again i am trying to create a program in unity pro from an Ab program. i have an FFL and FFU in rslogix 500 and need to use something like it in my Unity program. i have no idea as to where to start. the AB uses a source , a destination and a control register. i looked at the schneider website and this question was asked, schneiders answer was, no and that it would have to be created by the programmer. i guess my issue is that i can not figure out how to even start to program this. any help on this would be greatly appreciated. thanks

Unity has a FIFO block.

https://www.se.com/my/en/faqs/FA198859/

Thank you rankhornjp. i looked at that FB before but was confused as to how that might work like the FFL and FFU. if the FIFO itself (in unity) works the same as the control register (In AB) then i should be able to use this FB. Thanks again for your input.