You are not registered yet. Please click here to register!

plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
Try our online PLC Simulator- FREE.  Click here now to try it.

New Here? Please read this important info!!!

Go Back - Interactive Q & A > - Interactive Q & A > LIVE PLC Questions And Answers

Thread Tools Display Modes
Old April 5th, 2009, 05:21 PM   #1
United States

Archie is offline
Join Date: May 2002
Location: Orangeburg, SC
Posts: 1,916
Secret/Undocumented PLC Features

After making my latest video and discussing some features about Beckhoff and a few features that are undocumented or buried very deep, it came to mind that it would be good to start a thread and find out if others know of PLC features that are not well known. I'm NOT looking for hacks, cracks, or software pirating, but useful legit features that are typically only found by accident.

Does anyone know of some useful features that are not very well known? Looking for features to any brand of PLC.

This is my contribution on Beckhoff TwinCAT:
  Reply With Quote
Old April 5th, 2009, 07:33 PM   #2

rwy34ils is offline
Join Date: Mar 2009
Location: Edmonton, Alberta
Posts: 73
I would be happy if all the "known" features worked the way they should!!!!!!!
  Reply With Quote
Old April 6th, 2009, 08:04 AM   #3
South Africa

Rheinhardt is offline
Join Date: Oct 2003
Location: Pretoria
Posts: 39
LOL Agreed...
Rheinhardt Peens
  Reply With Quote
Old April 6th, 2009, 10:37 AM   #4
Ron Beaufort
Lifetime Supporting Member
United States

Ron Beaufort is offline
Ron Beaufort's Avatar
Join Date: Jul 2002
Location: Charleston, SC
Posts: 5,620
Greetings Archie ...

not sure if this is what you’re looking for, but here’s a trick that my more experienced students like a lot ... suppose that you’re out working on a system in the field and would dearly love to have something like a “simulator switch” to use for temporary troubleshooting purposes ...

the pictures show how to use the keyswitch on a PLC-5 or on an SLC-5/03 (or higher) to control something in your ladder program ... just turn the key between the Run and the REMote positions to switch between ON and OFF ...

disclaimer: obviously this is NOT something to arm Bubba the operator with – because you KNOW he’s going to turn that switch too far and shut everything down ... but used carefully, this can be a VERY handy TEMPORARY troubleshooting tool ...
Attached Images
File Type: jpg key_plc5.JPG (68.0 KB, 359 views)

2-B ?
Best regards, ----+----] [----+------------( )----
Ron | |
PLC Training Boot Camp - Retired | 2-B |

I once was lost, but now am found, was blind, but now I see.

  Reply With Quote
Old April 6th, 2009, 06:07 PM   #5
Lifetime Supporting Member
United States

TConnolly is offline
TConnolly's Avatar
Join Date: Apr 2005
Location: Salt Lake City
Posts: 6,151
Using that trick right now in a CLX. The first rung of the main routine in the continuous task uses GSV to get the key swtich position. Status is an INT tag.
Attached Images
File Type: jpg A040609A.jpg (20.0 KB, 263 views)
True craftsmanship is only one more power tool away.

That's the beauty of processors, they don't have emotions they just run code - The PLC Kid.
  Reply With Quote
Old April 7th, 2009, 01:47 PM   #6
United Kingdom

parky is offline
parky's Avatar
Join Date: Oct 2004
Location: Midlands
Posts: 2,097
Siemens S5 had loads of "un documented" instructions, well some I came across were not in the manuals.
some of their standard function blocks used system instructions not shown on any manuals I found.
In fact some i think were actual instructions but by using the way the ram structure was it was possible to create large DB's on the fly to fill the memory with a DB of several kilowords other RS instructions were used in standard blocks i.e. load a hex value into a flagword that is a MC5 machine code instruction then DO RSxx (process the instruction contained in the flagword).
It was possible to make self modifying code or transfer a datablock containing the MC5 instructions & create a function block nasty but have seen it done.
Once came across a system that checked how much memory was left in the plc & in the startup OB it created a DB just large enough to fill the memory, created the header for the block etc.
this was not to stop anybody from copying as if you uploaded it & tried to download it would say not enough memory.
but as a printer buffer on a critical process but then again unless you new how to re-load the plc you had great problems doing a mod.
Although not strictly an undocumented instruction I came across a function block that passed a timer (or the decimal value of a timer address) this foxed me for a while as the value was greater than 255 (the max number for a standard S5 timer, however I realised what the engineer had done.
Timers are addressed as an 8 bit word for the timer number, so 256 is timer 1 as it only processes the lower byte it sees the pointer as a "1". don't know what was in his mind apart from confusing other engineers but passing 0-255 would have done.
  Reply With Quote
Jump to Live PLC Question and Answer Forum


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
PLC features wish list monkeyhead LIVE PLC Questions And Answers 54 December 22nd, 2008 07:59 PM
PC to PLC Protocol TheRixta LIVE PLC Questions And Answers 13 December 17th, 2008 01:56 PM
Lightening effect on PLC patelbaroda LIVE PLC Questions And Answers 5 September 27th, 2007 09:53 PM
TEST your knowledge in PLC sqrz LIVE PLC Questions And Answers 11 June 1st, 2006 09:09 AM
Normally open or closed or... Phil Melore LIVE PLC Questions And Answers 15 February 3rd, 2003 08:14 PM

All times are GMT -4. The time now is 01:15 AM.