How to design a PLC?

I want to design a PLC using a PIC controller can someone help?

1. I need to know how I can split my program to have the user program and the PLC control program.
2. How to make the PIC controller read ladder diagrams
3 Any other software programming tips.

A nobel undertaking, even if just as a "Hmm, I wonder if I can do this?" type thing. Just a note on item #2. A PLC does not execute ladder diagrams. It executes a series of discrete instructions which, for the sake of an electrical diagram oriented programmer, is DISPLAYED in a ladder format to make the logic more visible. The logic exists in the type and order of the instructions even if no lines were ever drawn.

If you are used to an Allen-Bradley SLC500 or Micrologix (it may be true of the others but I can't be sure) you can see the individual instructions shown in another, "programmer friendly" form, the mnemonics (XIC, OTE etc). Even these letter mnemonics are for the comfort of the programmer only as it is NUMERIC codes which stand for these instructions is what is sent from the programming PC into the PLC and which reside in its memory.

Try this

PIC Forth

I know, this is Forth and not ladder.

Check out the Basic Stamp.. (yes I have the basic stamp II and the board of education)..

It's a blast... and they've already essentially have done exactly what you're looking for...

check this out:
http://www.parallax.com/

quick follow-up...

cool thing about the basic stamp is the language.. though once you get comfortable with them you could move onto c or assembly.
the basic stamps are great for prototyping.. work out the kinks and then use another controller...
In fact... the basic stamp II is a pic microcontroller...
pic 16C57C


Good luck!!!

Actually, it has been done before, check out Pic PLC

I agree the basic stamp is cool but the "real" thing is the picbasic compiler from Melabs. It's a really fast basic compiler and stamp compatible, great stuff.
Basic compiler

Good luck on the project!

plc

I don't know much about PLC pls help me

Benny, try scrolling to the top of this page and clicking on "learn PLCs".

Thanks everyone for the help. thierry2003 your link is not openning.

Any more ideas please post

XFile, I don't think you are serious or know what you are getting into.

I know because you are going about this all wrong. You should have a definition of what you want to do before you ask how to do it.

I know. I am a hard ***, but realize this. If xFile does not complete his PLC then all the time we spend helping him and the time he spend on his PLC is wasted. I think it is only fair that he demonstrates that he has the will and resources to see this project through to the end.

XFile, you are not the first to say you are writing a PLC program. No one that has posted on this forum ,including my own team, has has succeeded in making a finished and marketable PLC program. We have been working on ours for over a year. Our PLC works, but with too many limitations to say we are on the same level as a Control Logix.

I have not asked anyone on this forum on how to implement PLC firmware or compiler. I wouldn't expect anyone to have the answer.
If they did have the answer, I would expect them to give it. This kind of information is proprietory.

actually Peter

There is a thread or maybe more than one where the design of the PLC has been discussed. Just do the search for it. Basically the ladder compiler design isn't as much of an undertaking as the Programming
software design. The compiler design concept goes something like this.
Each ladder instruction (AND OR NOT Start of rung, store etc) is assigned an opcode. Inputs, outputs and memory bits are numbered.
The logic to implement instructions is stored in subroutines
whose address byte offset is the opcode for the instruction.
I really don't see this to be a huge problem. What I do see as a major and complex undertaking is the Programming software.

I have one here next to my desk. I think it is based on PIC
(based on format of the HEX files), it has LCD display, RS232 etc.
It has big DURANT label on it. One of supplier was kind to provide it but I didn't have time to look at it yet.

Peter Nachtwey

Thanks for your contribution I do understand what I am doing I have done my homework. The hardware is all setup I am using a PIC18FXXX.

I have to come up with a progam which is user friendly.I do not need a unit which I am the only one who can use it at the same time I have to find out if someone has an open source program running.

I will keep everyone updated on this project.