Fx0 Stl Assistance

[RalphW 0]

Greetings, I have a program that I am trying to translate... I have several rungs that have only -----[sTL S11] (or other status registers.) From my reading, I think I understand the STL function, but I have several questions. 1.) Does any STL Sx have to have a corresponding [RET]? I have quite a few nested ---[sTL Sx] and only see a single ---[RET]. Does the single [RET] serve all of the preceeding ---[sTL Sx]? 2.) What does the [sTL Sx] get you over a basic flag? It seems to me that I could accomplish the same task using SET, RST on a memory location to acheive the same effect. Or am I really missing something? 3.) My understanding would be that when a ----[sTL Sx] rung is encountered unless the corresponding Sx status relay is SET, the following section is not executed. At which point will the ladder logic continue executing? After the subsequent [RET]? (This makes the most sense to me based on the logic I have in front of me since it would only require a single [RET] statement to service multiple ----[sTL Sx] statements. In this case, it further muddies the waters between using the STL and a memory flag.) Thanks so much for you help in advance. Ralph

[Crossbow 297]

STL is what they call Step Ladder programming. Basically it's a flowchart. The STL instruction is the beginning of a step. Everything between that and the next STL instruction is the step. At the end of the step, it should set on another S bit. Then that step becomes active and the current one turns off. It's good for a machine with a specific sequence, as only the code in the active step(s) is processed. 1. No, STL instructions come at end of main ladder program, and they run sequentially to the one RET statement. 2. You could use SET/RST and M bits. The big difference is the reset of the active step is automatic when you enable the next step. 3. All the main ladder should be before the STL instructions. The STL should come right before any subroutines or the END statement. There is some help on Step Ladder programming in the FX Programming Manuals. If you're using an FX1S, FX1N, FX2N, or FX2NC, download JY992D88101 from www.meau.com, older FX series it's JY992D48301, and the new FX3U it's JY997D16601. All are also in the Downloads section here.

[RalphW 0]

That is strange...I have 2 seperate sections of STL statements in the logic I'm looking at. One near the beginning of the ladder and another near the end. If it were isolated from the rest of the ladder I would have understood it...but imbedded like that? So...I have about 8 ladder rungs of logic...a section of STL stuff...a return statement...much more ladder rungs...finally another section of STL stuff at the end. Hence my confusion. I've downloaded the documents you suggested, I even have the manual handy and have been going by it...it was just a wee bit confusing. Thanks, Ralph

[Goody 5]

The quick advantage of STL over SET RST is that the ladder is not scanned on inactive steps. Trouble shooting becomes easier as the problem will be in the active step. The program can be broken down in to little steps making it easier to follow. Several mini STL's can be active at the same time - like 2 or more auto sequences running. When you get used to all the limitations of STL - it is actually a great programming tool. I have hundreds of em out thier working away great year after year. If I ever have to go back to them - because I program them in little steps - I can see where I am straight away.