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Hi, I am trying to solve a puzzle where B3:0 and B3:1 are 3-digit numbers. I only have this diagram. Can you help me? I am completely new to ladder programming or Logix500 and simply cannot get my head around this. I suspect it is blatently obvious to users of this forum. Thanks in advance.
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Assuming all the bits are originally off go through the rungs noting the effect on the bits. The first two rungs are absolute. Calculate the others.

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Thanks, and thanks in advance for your patience (!) but how do I calculate the effect on the bits? I don't know what the numbers underneath mean yet.

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First off you should definately read the manual for RSLOGIX 500 available from Allen Bradley website.

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Move your mind from base 10 to binary. Then open the software and view the two registers (B3:0 and B3:1). First with a decimal radix and then with a binary radix. If you don't know how to do this then maybe less chicks and bar time and more class time is in order. The sooner that you get your head around words and and bits and how they are used the better off you will be in the real world (which differs greatly from the classroom). And yes- we are not giving you the answer for a reason. The puzzle that you have been given gets to the fundamental level of PLC programming and to some degree what's going on inside a computer. If you can get your hands on a book titled Code give that a read.

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Thank you for your reply. I can see you are reluctant to give an answer - I can respect your reasoning. I am a teacher myself and never give my pupils the easy option Yes, I was/ am looking for someone to spell it out to me on this occasion and entirely the reason behind me stumbling into this forum. Thanks anyway, and thank you for the links. I may continue to study a subject I have never heard of before and will never use again... or perhaps just give up on the puzzle. It is certainly a challenge and everyone loves a challenge! Either way, thanks and have a nice weekend.

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It's hard to know what level of help to give. What is your background (computers, PLCs)? What have you studied concerning ladder logic and the Allen Bradley version of ladder logic in particular? To what extent do you want to learn PLCs? Is it just enough to understand this little exercise or do you want to go further?

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Hi, before I stumbled on this puzzle I had never heard of PLCs or ladder logic at all and after this puzzle will probably never need it again. I teach young children so my background is very different to yours I should think! I am simply looking for the solution. I am trying to understand the puzzle but so far am struggling.

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See links... http://www.ronbeaufo..._frame_page.htm Click on sample lessons. http://www.plcs.net/contents.shtml http://www.plctutor....ay-ladder-logic Hint: B3:0 and B3:1 are word addresses, 16 bit words. Think binary. Addresses B3:0/4 and B3:1/7 are bit addresses within those words. They can be a one or zero ( True/False) (On/Off). Edited by Mickey

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The PLCs process information to control machinery and processes. Some information is processed as simple Yes/No or On/Off states called 'bits'. Other information is processed as numbers. The numbers in PLCs, like all computers, are made up of individual 'bits'. In the case of this example there are 16 'bits' per number. You are dealing with two 'numbers', B3:0 and B3:1 - don't worry about the meaning of those names if you aren't going further. The 'bits' which make up the numbers are shown under the symbols. The rightmost (as conventionally written) or 'least significant' bit of a number is '0'. The leftmost (in these numbers) would be labeled '15' - but these higher bits are not shown. The ladder logic processes the states of some of the bits to determine the states of others. The parts of a rung are in two sections. The rightmost symbols -( )- are the 'output' of each rung. All other symbols symbols to the left make up the states whose logical state are processed. A symbol -] [- is 'true' if the bit referred to is a '1'. A symbol -]/[- is 'true' if the bit referred to is a '0' If a 'true' state is passed to the right side then the named bit is 'turned on' or set to a '1'. If a 'true state' is not passed to the right side then the named bit is 'turned off' or set to a '0'. If two (or more) symbols are set on the same line then BOTH must be 'true' to pass a 'true state' toward the right. This is a 'series' or 'AND' circuit. If two states are linked above each other than if EITHER state is true the combination will pass a 'true state' toward the right. This is a 'parallel' or 'OR' circuit. At the output, if the output symbols are linked above each other then all the output symbols receive the same state. A 'rung' is the combination of symbols which pass a state toward the right side. The rung is considered as starting out with a 'true' state at the left side. Start out assuming that all the bits are '0'. Then begin evaluating the rungs. The first two rungs have no conditions so their 'true' state is passed to the right and each 'turns on' its named output. The other rungs have either 'series' or 'parallel' constructions. (Typical working rungs have many more symbols than these.) You will have to evaluate through all the rungs a few times as some symbols on the left side derive their state from outputs naming the same 'bit' later in the network (the collection of all the rungs.) I hope this is enough. Edited by b_carlton

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Thank you, both. You have been more than helpful and I appreciate the effort you have gone to to spell things out.

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Hello Me again; I'm still battling it out with this one. I have built this; Is there a kind soul who would explain what I should do next?

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What are you trying to accomplish?

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I'm trying to use the software to work through the rungs for me. I am looking for two 3-digit numbers and am hoping there is a 'run' button. I realise this is not a maths equation but honestly, I can't figure out where these numbers are going to come from!

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The program you are using on your PC prepares a ladder diagram based network so that it can be sent to a physical PLC for execution. It does not run the logic itself. There does exist a PC based emulator but it it obviously beyond your level. Do you have any concept of the computer storage of numbers? Do you understand how a series of 1's and 0s form a number? The words, B3:0 and B3:1 will, taken as 16 bit units, hold numbers once the solution of the ladder network is done. If that is not apparent then either put this exercise aside as interesting but not worthwhile or be prepared for a few months of study then come back to it. One source of study are the online classes available here. Good luck. Edited by b_carlton

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Thank you for the link. Ho hum. What a mind twist on a hot Saturday. Edited by Miangratten

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OK, one last help, but it is almost like cheating. Open the Windows calculator. Set it to 'scientific mode' under 'view'. The default method of showing numbers is decimal - 'Dec'. Type in any number, 3-4 digits will be fine, then select 'binary' - 'bin' What you see is the number but made up of ones and zeroes. If you do hand process the rungs then, with the display mode in 'binary' enter the final bits, the b3:x/0 (the slash is the way of separating the 'bit' portion of the address.) on the far right. Then change the display mode to 'decimal'. There is your number. You will have to do this twice, once for the bits in B3:0 and again for the bits in B3:1 Let's say you determine that bits 0, 5 and 7 will be set. You will enter '1 0 1 0 0 0 0 1' (without the spaces).

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I like that you feel it is cheating! You have offered so much and I feel so dense. I will work through the rungs again (my first try has resulted in all '0's!), and use the dec/bin function on the calculator. Thank you for your help. You must think I'm a complete nutcase.

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The program you posted in your post #1 is different then the one posted in post #13, is there a typo? ( rung number 1) Can you post the file here the .RSS file which is the program for the ML1100. Edited by Mickey

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Hi Mickey, I didn't spot a typo but I'm not surprised. Yes, I can see I typed in B3:0/7 instead of b3:1/7. I'm not surprised. The screenshot in post 13 was my foolish waste of a few hours setting up a programme in some software I knew nothing about... I thought there'd be a magic 'run' button that would tell me the value of B3:0 and B3:1. Much egg on my face?! The image in post 1 is from the puzzle and is correct. I would post the file you refer to if I knew what it was.

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The coil -( )- on rung 004 is the address B3:0/5 or B3:0/3? Also the -| |- on the rung is the address B3:0/5 or /8 and B3:1/5 or /8 Hard for these old eyes to read. Edited by Mickey

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I make the bit number on the far right of rung four as a 3. The ones on the left are both 8. ETA Hard for these old eyes to read too!! Edited by Miangratten

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Forgive me, b_carlton. The bits on my -] [- and -]/[- symbols are not only 1s and 0s. They are 4s, 7s, 8s and 0s. What am I missing?

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Here is your program in a real PLC in the run mode. ( as these eyes see it) See pictures below.