쉐도잉 연습: PLC Programming #4: Functions, Function Blocks & Organization Blocks Explained - 영상으로 영어 말하기 배우기

Hello and welcome back to the channel.

In today's video we'll be continuing our PLC tutorial series by looking at functions, function blocks and data blocks, and organization blocks.

The basic structure of how you create a large PLC program.

So of all the videos that we've done so far, this is the first one where much of what I'm saying will be Siemens specific

and there are a few other equipment manufacturers that use a similar structure to Siemens.

And there are some So I will try to call out what those differences are.

Broadly speaking, the topics will still apply to both and more universally any PLC that you're writing code for.

But some of the specific syntax will be Siemens specific in this tutorial.

Let's start from organization block.

The basic thing when you create a new PLC program, whether you're in Allen Bradley,

Rockwell or Siemens, you're going to be given main and it's going to be this special kind of

special kind of routine on both platforms.

Main is the PLC's main object loop.

It is the start here and go as fast as you can by default thing for both PLCs.

So if you remember or if you've seen the how PLCs work video that I published on my channel,

you'll know that we can go into a PLC and we can see how fast it's doing cycles.

That's this cycle time or scan time depending on what

scan of the PLC logic every millisecond

so that's a thousand times per second the longest one it's had is two milliseconds

and that was probably on boot so by default any code

that we drop in main is going to be getting processed as fast as the PLC can so

if we do just the very simplest piece of code we

could do to reorient everyone I have two input push buttons and one output light hooked up with.

If I just basically said, hey, when I push this button, I want this light to turn on,

I can put that in main main is a spot where you can technically write code.

But as we're going to talk about next, organizationally, you don't really want to put any functional code in main, all you want to do is call functions

and function blocks from main for almost any system that's going to be more than a few lines of code long.

So I put that code in and now I can push the start

and I can see the light turn on in the field.

So this is functional code.

But when you get to dozens or hundreds or thousands of IO points in a system, you don't want to put that stuff in main.

Instead, you want to create a new block, and here's where you need to decide between functions and function blocks.

And the number one thing I'm going to say the difference between functions and function blocks is, is memory.

Functions process things every scan, and then they make decisions about outputs, use them to calculate math and scale variables,

but they're not retaining anything in memory.

They don't have anywhere to store calculations in math that they did in the intermediate.

So functions are instantaneous.

So we'll just make an example function here

and we're going to replace this line of code in main

which is an organization block we're going to get rid of this

and instead we're going to call the example function

so this is the main loop saying all right go do this function

and then in this function we're going to evaluate here

and we're actually going to say okay

when I press the start button let's get rid of this momentary coil

and say when I press the start button set the light on and let's add a second rung of code

the stop push button, reset the light or turn it off.

Okay, so we've got this little function that says when the first button is pressed, turn that light on.

When I've got the second button, turn that light back off.

And then from main, which is my organization block, I'm saying, okay, call that function every scan of the cycle time.

Here you can see If I had hundreds of functions,

this main organization block can still stay fairly organized because all it's doing is calling specific functions in specific orders.

And if I had a function for every valve or every group of valves or every pump or every motor, it's still going to be pretty neat from the main organization block to go

and just see what gets called and in what order.

doing.

And they're very focused on a small subset of groups and functions.

So we'll go ahead and we'll download this real quick.

Okay, and now when I'm looking at main, I just see that the example function is lit up green, meaning it's getting called.

And if I go into example function, and I start monitoring it, I can see that the energy right is highlighted left here is green, and it's making it to these buttons.

So if I hold down the start button, and then release it, I've got the it resets it and it turns the light off.

So my function is working great.

And main, my organization block is calling that function.

Now, there's two other types of organization block we're going to touch on super quickly.

And then there's actually a lot more types of organization block, but they're a little more niche and nuanced.

So it's not really worth a high level overview covering them.

But if I go to organization block, I'm going to make one called startup.

And there's actually a block in Siemens called startup.

Alan Bradley, like I said, they don't have a special organization block for startup.

They have a bit that's like S colon FS, and it's a little different.

Logix 500 versus 5000, but they have a way to say, do this only on first scan is what they call it.

But the idea is the same.

Run this cycle of code exactly once when it starts up.

And the reason you might put in a certain state when they start up.

So like if I put the light here and I said, okay, the first time this code runs, I actually want that light to turn on because by default,

I'd like the light to be on until I come in and press the button to turn it off.

This is a spot where I could say right when the PLC boots up, turn that light on, but then it's going to stop getting called after that because it only runs on startup.

Similarly, one other type of organization block I here before we move on.

And you can actually see here a list of all the organization blocks that sort of come with TIA Portal.

But the other one I want to talk about is cyclic interrupt.

So you can have stuff that does not check that absolute as fast as the PLC can process, which is like every millisecond.

Here I can say, actually, I only want it to check 10 times a second.

So every hundred milliseconds or every half second.

So 500 milliseconds.

I can define how frequently I want

have issues with blipping sensors or things that happen way too frequently

and it's just creating noise for your program

or it's a little bit more processor intensive and

so it's actually harder for the plc to process it super

frequently things like pid loops have to go in cyclic interrupt blocks

because you can't update a pid a thousand times per second

and expect the the devices in the field to actually respond to that

so a cyclic interrupt is where you could say like okay

now I'm going to maybe get rid of the example function code where the stop push button is turning the light off.

And instead, I'm going to put this in cyclic interrupt, which means it's possible I'll have to hold that stop push button down for between, you know, one and 500 milliseconds,

depending on where in the scan cycle I am.

So I could drop this in the cyclic interrupt and delete it from example function.

And now I'm going to go ahead and download this.

What you'll notice is organization blocks, I did not have to add to main because organization blocks have rules about when they get called by default,

but you don't have to do anything special to make sure they get called.

100

Half second we made to get called every 500 milliseconds, and startup is going to get called when we boot the PLC up.

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So I'm going to download this and a recap of everything we should have happen.

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We're going to go ahead and continue.

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We're going to have to restart the PLC, and we should have the light turn on.

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and then we should be able to hold down the stop push button

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and that'll make it turn off but

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if I just click the stop push button we're not necessarily guaranteed to have the light turn off.

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Okay so I can sit here and I can click the stop push button momentarily

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and it's not turning the light off by default

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because sometimes I'm clicking it way too fast but

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if I hold it down I make sure that it gets scanned in

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that half millisecond time and that actually gets it to turn off.

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Okay so

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an introduction to uh organization blocks right we have a startup one

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that puts that light

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or pumps valves motors devices in startup state whatever you want them to default to

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when you first boot a system up main organization block is where we call all the functions

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and function blocks that we want to have scan every loop of the plc

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and you can use cyclic interrupts for things we've started covering functions a little bit,

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let's go ahead and do a little bit more, right?

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We can do something beyond just check if button pressed and set light on.

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Something like a very common thing might be scaling a analog value.

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So if we had a value that was coming in raw from a PLC, zero to 27 ,648, you know,

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basically an unscaled electrical signal on an IO card, take our raw input

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and we'll we'll make one up for this it's not a wiring lesson let's go ahead

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and define a global memory word let's say word

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and it's going to be an integer okay and let's just say

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that we have this raw input coming in

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and we want to divide it by 27 ,678 like I said 27 ,648 sorry it by 100.

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So this is basically like a very simple scaling function.

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Allen Bradley, they will call these compute blocks instead of calculate blocks.

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But the idea is the same, you can take this input one, you can divide it by what's your max span of the unprocessed signal.

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And then you can multiply it by 100.

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So you're basically getting a zero to 100 value, not by 100 by input three.

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There we go.

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in another tag that we'll call scaled input.

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OK, and we'll define that as a global memory as well.

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and that'll be the next integer.

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Okay.

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All right.

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So this is a good example of something you might use a function block for.

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There's no need to store this in memory because it's something that's getting calculated every scan of the PLC.

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So if you had a temperature here that's constantly fluctuating, you want to recalculate what the scaled input is every scan of the PLC.

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One other little syntactic thing it's important to call out is because this is calculating an integer, right?

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We made that a word.

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So it's not a real, it's not capable of holding decimal points.

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We actually want the internal math to be done as reals.

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And Alan, Siemens does this really nice thing with the indicated with these little squares that it's doing implicit type changing.

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So it's taking an integer value, it's converting it to a real, it'll do real math, and then I'll convert it to an integer on the outset.

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Not every PLC platform does that.

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So, you know, if this was just an

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be doing this in one divided by into and then rounding to the nearest integer.

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But the whole point of this is it's taking something

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that could be up to 27 ,000 scaling it back

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and then multiplying by 100 to basically get a zero to 100 % percentage.

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So we want to calculate a real just a little bit of PLC programming fun there for everybody.

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And let's go ahead and send that live.

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Basically now input is 59.

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But if this was some device in the field and oh, it saw a pressure spike or a temperature spike and goes up to 1800, it gets recalculated as a 65.

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So scaling of analog values is a really great example of something where a function does everything you'd need it to do.

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There's no need for function blocks here because that's an instantaneous calculation

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that you want to have done every scan of the PLC.

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So that's a decent explanation, I think, of functions.

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Now do want function blocks.

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But the most important use case is to keep in mind, do I want memory?

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Do I want something that gets stored and retained between cycles?

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Pretty simple analogy that I've seen before and had explained to me before is a function is like a vending machine.

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You walk up, you put in money, you get whatever you ordered out.

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And a function block is kind of like a bartender where they remember your favorite order

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and you can walk in and they remember what you got making you your regular.

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So if you're an analogies person, maybe that helps.

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But let's use an example of let's say I had not just one light hooked up, but let's go ahead into PLC tags and say I had two lights hooked up.

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Or, you know, really, you can put yourself in the shoes of like, hey, maybe I have hundreds or thousands of devices in my system.

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So I have so many pumps or motors or valves, in the same way.

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So now I have light zero and light one.

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And I want to write just a light function that is going to handle some code for all of them.

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So I'll just call this light and I'm going to make it a function block.

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OK.

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And the thing I want to retain the memory

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that I want out of this function block is how long each light has been active.

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OK, so I want to keep track of my input, which I'm going to come up here in the top section, which is where I can define inputs,

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outputs, things that need to both get passed in and go out.

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things, things that are going to get used inside of the routine only, as well as temporary and constant values.

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Now for the input, I'm going to say, well, that's actually just going to be the light input.

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Okay, so I'm going to tie whatever light this is keeping track of to this light input parameter

185

when I call the function.

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And then the main thing I'm going to output is going to be runtime minutes, and I'll make it a real so we can keep track of fractional minutes.

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And then in here, I'm going to make a very simple little bit of code.

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I'm going to check when my light input is active.

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Oh, I need the pound sign.

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But so we're going to have this light input and we're going to have it activate a retentive timer.

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Okay.

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And if you're following along with the series, you're probably familiar with the T O N R, which is a timer that keeps counting up and will retain how long a timer has been active.

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And we'll call this runtime.

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because it's happening inside of a data block.

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So we want it to get generated for every data block like this.

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Again, single instance, multi -instance, parameter instance, these are all just options of creating timers.

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The alternative would be you have to generate a new one

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of these outside of your function every time you made a new one of these.

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So we're gonna make it a parameter instance and it's going to automatically get dropped in, in, out.

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We don't actually need it getting passed in or out.

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video and then I'm gonna make this elapsed timer I'm gonna make it 10 minutes so that's 600 ,000 milliseconds

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And then we're going to come down here and we're going to move that time value of elapsed time.

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We're going to go ahead and move it into an intermediate value.

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So we'll take runtime, hashtag runtime dot elapsed time,

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and we're going to move it into an intermediate value that we'll just call runtime milliseconds.

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So this way we can have a tag.

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This will also be local static.

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int, that'll be fine, didn't just to make sure it's big enough.

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And now we have a milliseconds value we can do math on.

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So then we'll last thing we'll do is we'll make a calculate block, and we'll take runtime milliseconds, and we'll divide it by 60 ,000.

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Okay, and this will tell us our runtime minutes, whoops, runtime, underscore minutes.

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Alrighty, and then the function for this in one divided by in two, like that.

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And I think maybe the only thing we have to do here is say local output, local out, and real.

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And I'm a little surprised I'm getting this at all.

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Oh, yes, of course.

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So the reason I'm getting the red squiggly lines on this first one

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and down there is I accidentally put the hash signs in these tags when I define them up here, which is not correct.

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You need the hash signs when you reference them down here, those pound signs, but you don't put them on the tag names up top.

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So sorry for slipping.

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These tutorials are a fast.

221

So everyone makes mistakes.

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Okay, so to recap what we're doing here, we're going to pass in a value of a light, we're going to count up how long that timer has been counting,

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convert it to a milliseconds value, divide it by 60 ,000 and report back the runtime minutes.

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And we have two lights now.

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So we'll go into example function.

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And we'll say, all right, start push button is going to be button,

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let's say, will be tied to light one.

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I'll make these both momentary coils, and I'll just go ahead and delete half second and startup.

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We don't need those anymore.

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So basically, I'll even delete this calculate block.

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We really don't need that either.

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So basically the total code in the system now is

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when I'm holding start push button down the light zero should turn on

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when I'm holding the second button down light one should turn on

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and I have this function called light that should give me a count up counter for both those lights.

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But I have to do this last important step similar to the original function, I have to call them both.

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So here I'm going to say light zero and you can see when I dragged that function block that I just defined.

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into main to get called, it automatically said, hey, you need to make a data block to store the memory associated with this instance of your function block.

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So I'll call this light zero data block.

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And then I'm going to make another light.

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And this is where you see the power of function blocks.

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I'm going to make another light and call it light one data block.

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And I'm going to tie this light input to light zero.

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And I'm going to type this light input into light one.

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I'm going to download this PLC function and if we did it right

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and that's a big if I should have two different timers here

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That when I hold down the two different buttons They're both going to activate different retentive timers

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and I get the this functionality of seeing how long they've

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been running for free Twice even though I only wrote the code once

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so I'll hold down one button here

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and the timer does not count up I'll hold down the other that timer does not count up epic

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we got the wrong type here.

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So yeah, so we're calculating a dent, which means an integer value, which means it's going to be rounding to the nearest whole minute, which is why nothing happened on the seconds order.

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Let's go ahead and make that a real and download.

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All right, but let's go back to main now that we're calculating reels.

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And actually, you can see immediately, we have these fractional values already, which is cool.

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So let's try this demo.

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Let's hold down light one.

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Okay, and now let's hold down light zero.

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All right, and hopefully you can see, this is a very simple example because I'm trying to go fast for this YouTube tutorial,

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but we got retentive timers to tell us how long these lights were running for free by writing general code,

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generic code in a function block that can be extrapolated away to many instances.

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So if I made a thousand light objects, I could call all of them from main,

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And I would get this counter of how long they've each

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been running just by tying the correct input to each of those data block instances.

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So that's kind of the main reason to use function blocks and data blocks instead of just plain old functions.

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That's how organization blocks work.

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And again, PLC to PLC, these individual things can get called something different.

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But the main way they work and the main thing they do are pretty universal across every platform.

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So I hope you found this tutorial useful.

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been enjoying the controls and automation series.

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As always, let me know in the comments if you have any questions

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or what you'd like to see more of on the channel.

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Please consider leaving a like on the video and subscribing to the channel, and we'll see you next time.

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Thanks.

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Bye.

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