Function Calls in Step7

farmboy_jon · Oct 6, 2002

im having some trouble in one of my labs, what im stuck on is this...

i need to turn on 3 outputs when the plc goes into run mode, using only two STL lines of Code.

I know i need to program this into OB100, im just not clear on how i can turn on 3 outputs regardless of anything else

after turning these outputs on i also need to turn them off when an input is sensed and turn on 3 more outputs using a function once again.

What im stuck on here i think is how to go about writing and calling functions
thanks in advance, jon

rsdoran · Oct 6, 2002

I will probably get this wrong but what the L, if you dont try you never will get it right.

I do ladder when I get the chance to do anything, if you were to start 3 outputs at once with same inputs then you "branch" the outputs
EX:



-------|input|---------------------(output1)---

                               |

                               |---(output2)---

                               |

                               |---(output3)---

Using STL (statement list) it will be something like:
LD input1 = output1
AND output2
AND output3

Note: I do not know STL and have not got the books here to look it up, hopefully though I am close enough for you to get the idea.

ALSO: OB are blocks with instructions, you create FB (function blocks that call the OB

See if this link will take you to the Software manual http://www4.ad.siemens.de/dnl/TQ1MDAyMQAA_1117858/Bhbv40_e.pdf

Others will offer more/better advice...be patient and post what you have done and where you are having problems.

farmboy_jon · Oct 6, 2002

Thanks for the help, but im not sure you understood what i was asking

I need to turn on these outputs regardless of any input conditions.

I understand what you were saying, branch at the end of the ladder and add more outputs.

It doesnt seem to want to let me turn on any outputs without an input of some type.

thanks

rsdoran · Oct 6, 2002

Oh thats easy then ...dont use the PLC to turn them on if you need them on when you start the machine, hardwire them to start when machine is initialized.

IF you want them on via the plc then use a start machine sequence to turn on an internal bit that is on as long as power is good or estop is ok (your choice).

GNewson · Oct 6, 2002

Why not use a first scan bit to latch your outputs? I'm not fluent with STL, and have only used S7-200 software, so I can't help with the code.

farmboy_jon · Oct 6, 2002

hey, i think your right about latching the inputs, i never thought of that

so if i just did the following in OB100 it should work?

S Q output1
S Q output2
S Q output3

then id just need to make a function that resets each of these and call it to shut them off?

i think im gettin there, thanks guys

The Dark Knight · Oct 6, 2002

Here ya go
1st, create fc 1
s q1.0 ( whatever your outputs are)
s q1.1
s q1.2

make sure that you use the s command and not the set command or you will have problems.

in OB100 (STL)

CALL FC1

Eric Nelson · Oct 6, 2002

You're contradicting yourself Jon...

"I need to turn on these outputs regardless of any input conditions"

Yet earlier you wrote:

"after turning these outputs on i also need to turn them off when an input is sensed"

What if the input is sensed at powerup?

Instead of latching (which will work too), maybe just change Ron's (rsdoran's) example to use a "NOT" contact?

Code:

[size=3]
      INPUT
-------|/|-----------(output1)---
                 |
                 |---(output2)---
                 |
                 |---(output3)---
[/size]

beerchug

-Eric

farmboy_jon · Oct 6, 2002

sorry eric, what i meant is that the input has to go from off to on to turn these off, as for turning them on, it should occour despite any other conditions

not sure if your following me, but i think i've got a better understanding of what i have to do now

thanks for all your help, things are getting clearer and clearer

rsdoran · Oct 6, 2002

Then look at Eric's example a little close...using the XIC will make the rung true..ie ON when the input is OFF and when the input is ON the rung will go false..ie the outputs will turn off.

This can be confusing but in time you will get it.

Eric Nelson · Oct 7, 2002

You might want to investigate "edge detection"... See our lengthy discussion about that in THIS THREAD

beerchug

-Eric

Hey Ron and Jon, ever think of getting together and opening a surf shop?...

(Those who don't get that joke, click HERE)...

rsdoran · Oct 7, 2002

Believe it or not I know the people that started that, they are heavy into T shirt sales and travel to fairs etc, I was in the amusement business (actually grew up in it) so had the pleasure of meeting them many years ago.

Eric Nelson · Oct 7, 2002

Continued Off Topic...

....heavy into T shirt sales....

And I've bought my share! Great "work shirts" as they last a long time... Ron Jon's original Beach Haven, NJ store was always a yearly stop while vacationing on LBI. They recently built a huge new store on the same property.

Additional useless stuff... I knew the owners of "Things U Like" in Manahawkin, NJ who knew Ron back when he started out.

beerchug

-Eric

jvdcande · Oct 7, 2002

farmboy_jon,

the only way to activate more than 2 outputs with only 2 lines of STL code is bij transferring a bitpattern to these outputs. Since S7 works with doublewords at most, these outputs must be positioned within the same doubleword. This is basic info! The key phrase for your question is: check that bloody manual (or your courseware in case you're a student, which is probably the case).

Jean Pierre Vandecandelaere
Instructor PLC - SCADA

farmboy_jon · Oct 7, 2002

thanks Jean Pierre, i think i've got it now, i hope anyway

L 2#10110000
T QB 124

this should turn on outputs 124.7, 124.5, 124.4

correct?

i am a student, and yes i should know this stuff, but its not clear to me thats why i was asking

your help is appreciated

Function Calls in Step7

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