I'm new to Siemens and I'm testing with a simple example to toggle an output every two seconds.

I understand there are many solutions to this example.  However, my concern is that the toggle every only occurs sometimes.

Why does Q only go TRUE sometimes?

Maybe I don't understand yet the execution of Main or function blocks within ladder.

Thank you for looking at this .

then retested to do the reset

 Yes, but in series with ToggleOutput - which was reset above.

resulting in always having the output at 0

 I'm not sure that's correct - if you look at the trace, %Q0.0 (MyDigitalOutput) is nonzero.

Sometimes it's true, sometimes it's false, but the toggle is not occuring when expected (every two seconds).

AutoGen_3976700

Thank you for looking at this .

then retested to do the reset

 Yes, but in series with ToggleOutput - which was reset above.

resulting in always having the output at 0

 I'm not sure that's correct - if you look at the trace, %Q0.0 (MyDigitalOutput) is nonzero.

Sometimes it's true, sometimes it's false, but the toggle is not occuring when expected (every two seconds).

 You should read Gustavo Banchettis post again, and think about what he's writing and also look at the example code he posted.

When you use a COIL, and have the same Tag in a COIL in several places, only the last one in excecution order is dominant.

I'm primary a C programmer, so most of this terminology is new to me.

Gustavo's solution is simple and correct. Output = (Timer.Q && !Output) || (!Timer.Q && Output).  Maybe this is the difference between using coils and set/reset.

I see he's saying manipulate the output on one rung reacting to the event rather than multiple rungs.

However, in my original example when the event occurs - I set the output and reset the toggle variable on the second rung.  My assumption is the third rung would not execute - is that the case or am I wrong to assume that?

AutoGen_3976700

I'm primary a C programmer, so most of this terminology is new to me.

Gustavo's solution is simple and correct. Output = (Timer.Q && !Output) || (!Timer.Q && Output).  Maybe this is the difference between using coils and set/reset.

I see he's saying manipulate the output on one rung reacting to the event rather than multiple rungs.

However, in my original example when the event occurs - I set the output and reset the toggle variable on the second rung.  My assumption is the third rung would not execute - is that the case or am I wrong to assume that?

 Your assumption is wrong. The last point of the Tag write is the dominant one, all before it are basically useless. So when using a COIL, you should write the tag in only one place, and have the needed conditions in front, Just like Gustavo has show in he's attachement.

Coding PLC's is a different ball game compared to computers. There are legalities that are unique to PLC's and how they execute code.

AutoGen_3976700

I'm primary a C programmer,

 No offense but that has nothing to do with it. who more, who less, we all are.

I'm still confused.  I would expect the output to toggle on and off.  Am I using the TON correctly?

Maybe I shouldn't be using Q as the input to IN on TON.

AutoGen_3976700

I'm still confused.  I would expect the output to toggle on and off.  Am I using the TON correctly?

 When you use the .Q of the timer to activate the timer, the .Q state doesn't change in the next network, because it's already reset in the previous network, when the timer time has elapsed.