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.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!

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

PLC training tools sale

Thread Tools Display Modes
Old May 17th, 2006, 07:51 AM   #1

sparky64 is offline
Join Date: May 2003
Location: Newcastle upon Tyne
Posts: 127
Just a question - I/O Mapping to Integer files

Some of our PLCs' have code written so that the I/O files are mapped unconditionally into integer files, and the bits or words of the integer file are used in the code, instead of the actual inputs or outputs. Can anyone tell me why do the programmers do this, because it becomes a pain to fault find on, especially if the documentation is not what it should be.

  Reply With Quote
Old May 17th, 2006, 07:58 AM   #2
United States

jstolaruk is offline
Join Date: Dec 2004
Location: Detroit, SouthEast Michigan
Posts: 3,346
Sometimes its not the programmers choice. I've had customers that actually require it as part of their controls specification that real I/O be mapped to internals and that internals are to be used in programming. The last time I ran into this was at a Delphi plant in Saginaw MI on a disk brake caliper assembly machine. It was a Modicon application and they stated that if they lose an input or output the eletrician just has to go to the one rung where the real I/O point is mapped and make a change to use a spare.
"You can live to be a hundred if you give up all the things that make you want to live to be a hundred." Woody Allen

Last edited by jstolaruk; May 17th, 2006 at 07:59 AM. Reason: spelling
  Reply With Quote
Old May 17th, 2006, 08:07 AM   #3
Lifetime Supporting Member
United States

rdrast is offline
rdrast's Avatar
Join Date: Apr 2003
Location: South Carolina Lowcountry
Posts: 5,355
There are lots of reasons.
One may be that the OEM has many 'similar' machines, so writing the entire program referencing identical integer file points means that the core logic never changes. They merely connect up the actual physical I/O to the 'mimic' points in the program.

One example of this could even be as simple as where a manufacturer makes a machine with all pushbutton control, and an upgrade that has touchscreen control. By mapping to internal points, either set of 'physical' inputs can be used.

Another reason could be when someone is developing a program, without any idea what the physical I/O layout will be (actually, that's pretty common, believe it or not). Again, once the logic is complete, the I/O can be mapped later on.

Then there is the case where I/O points are going to be shown on an HMI. In some cases, HMI's cannot directly read all I/O points, but even when they can, it is more efficient (communications wise) to group data together into blocks that can be read at one time.

One more reason, is that with more and more asynchronous scan PLC's showing up, is that sometimes it is important to make a scan-invariant copy of the input table, and sometimes even a scan-invariant copy of the output table in order to simulate PLC's with a synchronous I/O scan.

Just a few reasons off the top of my head, there are many more.
  Reply With Quote
Old May 17th, 2006, 10:13 AM   #4

marius is offline
marius's Avatar
Join Date: Apr 2005
Posts: 239
well... i'm using this method quite often, because of simulation purposes... 1) build architecture which allows to switch between various inputs or outputs 2) simply invert bit tag to set mode of real ai,ao,di,do,tm/ virtual ai,ao,... and still let whole functionality unharmed - this also helps me if somebody need to try immediately different settings of gas/ oxygene for burners etc.

(and yes rdrast, to cross them easily too)

and there may be another 'historical' reason (more like custom) - some platform i/o cards in past wasn't able to send data fast enough for cpu or if they was, it ate so much cpu time - so the trick on 'small application' is: not to communicate so hastly with i/o - today, cpu's doing this behind user code
  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
Controllogix elledge LIVE PLC Questions And Answers 43 February 12th, 2014 02:55 AM
Shifting I/O Modules, Slots: RSLogix 500 Question mbd0722 LIVE PLC Questions And Answers 8 February 4th, 2012 03:56 PM
Remote I/O Flex I/O Quick Change Tooling Fixture TamHoNutech LIVE PLC Questions And Answers 1 September 29th, 2005 05:46 PM
kv300 I/O question Unregistered LIVE PLC Questions And Answers 0 May 26th, 2005 05:03 PM
String Files VS Integer Files Steve Meisel LIVE PLC Questions And Answers 5 September 16th, 2002 07:09 PM

All times are GMT -5. The time now is 04:07 PM.