FIFO (FFL/FFU) instructions

[KIKO 0]

could u please explain how those instruction work....thanx

[TechJunki 0]

Doing a search of this fourm will give you many different threads on this subject. Here are a few of them. You may want to read through them and then come back if you have any more specific questions. HERE and HERE

[sathya 1]

hello sir, u can go in www.patchn.com were u can find sample PDF of the instruction

[KIKO 0]

Hi TechJunki I studied your sample program for FFL/FFU..I want toask u: 1-when B3:0/2 transition from false to true the value on N7:0 should be transfered from N7:0 to N17:0...right??? 2-When B3:0/2 transition from false to new again then the value of N7:0 will be transfered to N17:1 OR it will be transfered to N17:0 after N17:0 has been transfered to N17:1??? 3-suppose after the above two transitions...what the position value should be...is it 2 or 3 or something else???? 4-Suppose after the above two transitions....now the B3:0/3 transition from false to true..then which value should unloaded from the stack to the address N17:60...is it the value on N17:0 or N17:1? Thanks alot

[BobLfoot 302]

KIKO - I did not find the exact example of Techjunki's to which you refer , but I will attempt to answer your questions as best I can. 1. When the Trigger of a FIFO goes from false to true the 0 register is loaded with data. In the case you refer to N17:0. 2. Since it is First In First Out this is the true nature you need to be concerned with. From what I recall and I can't test this right now the new value is added to N17;1 and the data shift ocurs when unloading. 3. After the two transitions described the POS value would be 2 and would be pointed at N17:2. 4. IF I rremember correctly the value of N17:0 woould go to N17;60, then N17:1 would move to N17:0 and the POS would be POS - 1. Curious why you are so concerned about the inner working of FFL/FFU. I usually treat them as black box object and all works just fine. Just remember to use in pairs or make allowance for when FFL goes DN.

[KIKO 0]

Thanx Bob...Actually I used to deal with FFL/FFU as a black box too..but this time I have a problem on my process which need a deep understand for those instructions .. I still have one more question. when the rung of the FFU instruction goes from false to true then N17:0 will go to N17:60..what will happen when it goes again from false to true??? will the new value of N17:0(after the shifting) will go to N17:61...Or it should go to n17:60 after the previous value of N17:60 is shifted to N17:61???

[Smoke 0]

As I remember it until the array is full it moves to N17:60 then N17:61 then N17:62 until the array full then it moves N17:0 to N17:60 each time and kicks off the last regy in the array. I remember this because of how differently it acted from GE's Array Move.

[KIKO 0]

I think now I have a good idea about the deep details of the instruction... My question now..suppose that the position value is 3 then suddenly went to zero...what that should mean?..I guess that there was a 3 false to true transitions on the FFU rung...isn't it?

[KIKO 0]

hellooo any help will be appreciated thanx

[Chavak 2]

Hi Kiko, Your assumption is right, there might have 3 false transitions on the FFU rung. --> This can be verified by checking the pos value in the Control Word. [R6:X.pos]. A value of zero in the control word denotes there was a transition on the rung, and unload was occured. Other than this, only way I can think of the data lost is some other logic writes a zero into your FIFO words, I guess you do not do that. ______