This is the old old old school of programming.

Focus on this question: why you need to use one million of merkers (bits) each step and have to become crazy when you have to re-init them, to check them , etc ?

Why don't you use a NUMBER ? A stupid integer that you set every time like this:

CASE sequencer_var OF

10: Wait for Start button. When pressed set sequencer_var:= 100

100 : DO Running, when finished set sequencer_var:= 200

200: DO Pause, when finished set sequencer_var:= 300

300: DO Reposition, when finished set sequencer_var:= 10

END_CASE;

Need to externally reinit the cycle ? set sequencer_var:= 10

Wanna know what ur system is doing ? Just look at that number

I think that every serious machine should do in this way, but this is my egoistic point of view :D

Hi!

My problem with setting and resetting bits for creating a sequence was that it is very cumbersome and error-prone to modify something or add a step in the code.

My problem with using an integer for creating a sequence was that I could not do cross-reference on a comparison instruction like step_int = 5 in Step 7 (as far as I know) to find a certain step in a sequence (important for the maintenance guys).

Now I use both. I create a DB with step bits which are set and reset based on a step number. When the condition for the next step is satisfied, the step nr is incremented and thus the next step bit is set, the others are reset. Cross-reference is easy, inserting a new step means inserting a bit in the DB.

The sequence FC is in ladder for the maintenance guys, while the bit setting based on the step number is in SCL.

For applications where a state machine is needed instead of a sequencer, I use something similar to what Jeff described above.

I do everything as state machines as I find it difficult to handle interruptions in sequences (what happens if there is a drive fault during sequence step X?).  It is more work, but in the end I find it easier.  Just me maybe.

As I tell my engineers, 25% of control engineering is making it work.  75% is what to do if it does not.

Jeff Casagrande

...25% of control engineering is making it work.  75% is what to do if it does not.

(smile)   +    

Hi!

Jeff Casagrande

I do everything as state machines as I find it difficult to handle interruptions in sequences (what happens if there is a drive fault during sequence step X?).  It is more work, but in the end I find it easier.  Just me maybe.

I think that this is more like application dependent. We build simple assembly stations so for us a sequencer is easier to use. An FC for each state would be an overkill in our case. 

Jeff Casagrande

As I tell my engineers, 25% of control engineering is making it work.  75% is what to do if it does not.

100% agree!

5hane_B&H

I have never programmed in SCL, only used ladder. Is there a link for a tutorial and some program examples?

 FYI

looking-for-beginners-guide-to-scl-for-the-s7-1200

s7-scl-v5.3-for-s7-300400-getting-started