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It starts on page 12.16 in versions 4.5 and 4.6. I am hoping that those methods will not require any changes to use.

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There's a version 4.6? When did it come out, I thought I just checked last week... I only have 4.5!

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I didn't make a big deal about it, it was mainly the addition of a few new problems and correction of some mistakes.

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Hello ! Think I start to understand what "delayed update" means .. Thought ST1X were just "another bit" but it actually keeps its value for one aditional "turn" of the program execution ?! (On the Allen Bradley.) Could not find such a function for the Step-7 and don't know if it exist at all, but I belive I got the same functionality running using set and reset on the outout (?!) http://arne.dyndns.dk/plcbook/Chapter-12/Figure-12-24/ By the way .. is it any progress with the Omron/Telemechanique etc .. translation ?? (I think such translations for diferent brands and program systems could lead to som "average program code" that can be used for nearly any PLC.) By the way, thanks for the comments because it's booring to work on things just alone. Best reg Arne.

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Actually those bits are just internal memory bits - nothing special. The reason for the delayed update is that when the state bits are changed immediately the logic may not be solved correctly.

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I run into an interesting problem in page "plc states - 12.36", Rev 5 of the book. I chosed this problem because it looked "so easy", but actually it apeared to be "so difficult". Does this progran code really run on Allen Bradley PLC ? (It might be something that I have not understood, but for me it looks like it is "something" with the logic in this program". Woluld be happy for any ideas or suggestions. http://arne.dyndns.dk/plcbook/Chapter-12/p...c-states-12-36/ Best reg Arne.

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By the way .. the problem in 12.36 prog 4 is only due to the use of inpu B and C more than one time. If it were like 12.37 prog 5, there would be no problem at all. here it is used 6 different inpust, A, B, C, D, E, F I think this should work easy at any PLC, allmost unchanged. Will give it a try ..

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Program 12-37 (rev 5) seems to be working without a problem. (Unchanged, near identical code seems to working on Allen Bradley and on Siemens step 7. I guess that the problems in 12-36 is just because of a "misprint" and that it was not the intention that 12.36 should be so much more difficult than 12.37 ? http://arne.dyndns.dk/plcbook/Chapter-12/p...c-states-12-37/

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You should be able to enter the program on page 12-36 using normal outputs (switching internal memory bits). The program you linked to seems to be using S/R (flip-flop) outputs.

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Yes, thats right. The 12-36 program produced loops and "flickering". Because of this I tried to change it to SR flip flops. (To avoid the problems.) The 12-36 proram did not work for me "as-is" and I think there is som indications on logical faults in that program that is in the book, but of course I could be wrong (and I have never tried to program an Allan Bradley.) The problems experienced with the 12-36 program is explained in the link to the modified program with the SR flip flops (As far as I have tested it, I believe that the SR flip flop variant does not have the same problem. On the other side I belive it is not according to the Boolean equatation after the modification.

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Hello, I should have read your earlier post more carefully. The state diagram does describe a potentially problematic system because of the transitions with C&B and C+B. If C&B is true there would be a loop effect. Although it should not be confused with an endless loop. Each scan of the ladder logic it would alternate between the two states, ST2 and ST3. So each state would be true for one scan of the ladder logic. This would stop when either C or B became false, or A became true resulting in transition T1 and moving to ST1. Hope this helps, Hugh

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Wheather you release B or C first, you will allways end up in St3. After the flickering and the alternating between ST2 and St3 you will allwaus end up in St3. It is locked in St3 and it can not come out of it. I tried to set in a positive flange detector, but even with that it was still stuck in St3. To come back to St2 "as is", and to avoyd jumping back to St3, you will have to releace B and C in the same fraction of a milisecond. Because of this it will be neccessary to build in some "tracking mechanism" to keep track om "where it came from", as long as input B ans C are used like they are. Using some other inputs as criteria for the transactions would also clear out the situation. The problem is actually rather interesting, because the boolean equatations is describing a logical situation with no "time factor" and no "sequences". The real life situation contanis a "time factor" and things that happen as a "sequence". Best reg Arne.

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There is a mathematical method for handling this problem, but unfortunately I can't remember what it was called. I started my working life designing first generation computer controlled telephone exchanges 40 years ago. We were initially working with DTL (diode-transistor-logic) before moving on to the now ubiquitous TTL circuits, but even they had (by modern standards) relatively slow switching speeds, which meant that the Karnaugh map alone was not sufficient to describe the logic accurately. Maybe this will jog somebody else's memory and they might remember what the method is called.

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I see your point (and I will modify the example to make it more well behaved. However, for now, if you want to reach ST1 you should be able to do it with the method below. 1. Set B and C true to start it cycling between ST2 and ST3. 2. Set A true and the diagram should start cycling between ST1 and ST2. (Note: when transition T1 is true it blocks ST3 from turning on.) 3. Set 'B' false. If the system is in ST1 it will remain there. If the system is in ST2 it will move to ST1 and remain there.

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Hello ! Procedure as described above tested at Siemens Step 7. Works as described and expected. By the way, I think the book is great in the way it explaines the theory behind flow chart and state based design. Thats a thing I think I really has missed, a book that explain these things. There is really some books that explain syntax and not much more. When students ask "but how do you really think to make a PLC program" I think I have used to answer something like: "Well you have to know a lot of syntax and a lot of exaples and use these in a creative way". This book is much more methodical so it's very interesting to work trough the theory and the examples, and actually the theory and the methods is so "general", so I believe they can be used on allmost any PLC. (Even though adjusting some minor syntax details to make it work.) Of cource there is "an other story" about more specific Siemens and IEC 61131-3 related things like OB's, FC's, FB and DB's, program modularisation and things like that. My personal point of view is that some more Simens spesific books does to much out of this programming elements, explaining to much syntax and syntax oportunities, without any really good explanation of how to use this syntax. My personal point of view is that it might be a good idea to just let Siemens Step 7 ba as easy and classical as it can be, If you want it to be like that, and then rather to add on the more Siemens spesific things, on al later stage, "on top of that". ...Just some general reflections about the more general and the more specific related to PLC programming... Best reg Arne.

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In general programming (of any sort) can be viewed as an art, or as a science. If you learn to program yourself (as I have) you tend to learn it as an art. And, I must admit that it is very enjoyable to try new things and find creative solutions to difficult problems. However, if we are to engineer a system it must be done through careful scientific design. This is where the techniques in the book can be useful. It is also why the IEC 61131 standards hold so much hope, because they provide tools to structure programs. As an analogy consider a basic circuits or statics course. Students do not just dive into the problems and try to find a solution. They learn methods such as node-voltage, methods of joints, etc. Without these methods they might be able to solve the problems, but with them they can do so much more, in a shorter time, with more reliable results. I have only proposed a few methods in the book, but there are so many other possibilities for structured program design.

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Hello ! I think that quite many of those books I have found for learning to program Siemens Siemens Step 7 start out with the methods of building and using moduls, OB's, FC's, FB's, DB's etc before you learn almost anything else. For personell with background in programming and doing object oriented things like C++ it might be obvious what these things can be used for. For maintenance personell not used to these methods it might be not so familiar and possibly a bit confusing. It can be rather difficult to explain the use of FC's and FB's as the foirst step in the process of learning PLC programming. I think it is a good idea to start to learn and undertstand the more general terms and the use of each block before you extend these basic methods using a more structured aproach. In this way, from the point of view as I see it, the existing Allen Bradley book could be a great Step 7 book if it just got an amendment (or something like that) with the Step 7 implementations on the program codes and a rather easy and short amendment "how to expand this basic to also include more stuctured elements a la IEC 61131". Just some ideas .. Best reg Arne G.

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Why not consider giving up Siemens and going with AB in your classes? AB is dominant, and will continue to be so for awhile. Jim

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Jim, you're not following what he is trying to do. hugh Jack has written an excellent book he uses to teach a college level class, and his book is centered around Allen Bradley. Arne is trying to recreate the lab exercises for other vendors, like Siemens and Mitsubishi. As for AB being dominant, only in the US. In the rest of the world Siemens and Mitsubishi and Omron far outnumber AB. This is a global support forum... Siemens actually sells more PLCs than any other vendor when considering worldwide sales.

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Has anyone given any thought to 'translating' his book to work with Automation Direct PLCs or even to work with think and do (flow charting)? There is a lack of materials / examples out there for using WPLCs and the Think and Do software. Just a thought.

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