Step 7 Online funny problem

sohwel · Oct 18, 2008

Anyone know what cause this problem or is it only happen to me.

The move block are not execute, i check by monitoring the output of the move block

OZEE · Oct 18, 2008

I don't use Step 7, but there appears to be something different about those instructions in the dashed blue lines. Have they been inserted, but not accepted/assembled yet??

mrmss · Oct 18, 2008

Chances are that the statements are being executed but the screen update in S7 can be unpredictable at the best of times.

Sometimes it depends on your laptop CPU, or your network traffic, or the speed of the connection to the PLC.
Sometimes if you click just before or after the move, it might go green! Once it wouldnt update anything until I did a reboot.

Best thing is to do a VAT table or use the monitor on the bottom tab to see the values in your registers.

S7Guy · Oct 18, 2008

Siemens ladder representation is woefully inadequate. Often, people will come to me with similar issues, and I just swap it to STL and show them that the code is executing just fine. I know people say that ladder representation is easier to troubleshoot with, but I've found that if the network contains non-boolean instructions or more complex logic, it's more of a hassle than its worth.

So, switch to STL, and analyze the RLO and accumulators, and it will show you the correct status.

L D[AR2P#0.0] · Oct 18, 2008

This problem is normally be due to the RLO not being evaluated in the previous network(s).

sohwel · Oct 18, 2008

the move block it not executing, i check it with the VAT table, any changes to the move block input does not change it output.

however if i put another true_b in parallel with the existing true_b the move function will execute, this is how i left it.

L D[AR2P#0.0] · Oct 18, 2008

Here is your problem reproduced. As already stated, there is a coding error in the network(s) prior to the one you have posted.

manmeetvirdi · Oct 18, 2008

Wow
L D[AR2,P#0.0], you have produced a exact error!!
Can you post your error code !!??

L D[AR2P#0.0] · Oct 18, 2008

Code:

	  SET   
	  S	 #bTrue
	  AN	#bTrue

manmeetvirdi · Oct 19, 2008

Thanks for the error code
I was very much eager to know as to what can make the things like this happen.
And found that this happens if you write half the code in STL and other half in LADDER.

Same thing written completely in LADDER does not seems wired !!

Nick B · Oct 19, 2008

I'm betting the destination DB does not exist or is write protected. Go to online blocks and check if the destination DB is there. Thus the move instruction does not execute and thus the RLO.

manmeetvirdi · Oct 20, 2008

Hi there NickB

Representation in LADDER does not comes as shown in post#1, if I use bit as a DB.
If I use DB with MOVE block then also representation does not come as in post#1.

cjd1965 · Oct 20, 2008

Hi I agree with L D[AR2,P#0.0] the block is not being scanned by the PLCThis is because the preceeding block is not passing control to this block.

Have you tried putting

SET
SAVE

at the end of the preceeding block?

userxyz · Oct 20, 2008

I had the same prob... wrote things in STL and the LAD network after my stl code did also this weird thing. I just wrote SET at the end of my stl code and it was solved.

sohwel · Oct 20, 2008

the destination block do exist, the function block is written in STL and only two network that uses LAD. I could not find the actual cause so did a L and T. problem solved.

Step 7 Online funny problem

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