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jagwinn

Elementary question

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Hello all, Me again with a basic question (or a question about the basics). The only instruction I have to learn by is for a 1 line circuit with 1 input and 1 output. The instruction says to double click the "?" mark and type I:0/0 for the input. It then says to double click the "?" on the output and type O:0/0. This program runs O.K. in the emulator. No instruction is given for a second circuit, so I tried on my own and on circuit 2, I put an input as I:2/2 and an output as O:2/2. This did not work. The window at the bottom that guides your corrections accepted as correct when I put the I:0/0 and the O:0/0 on BOTH circuits, but, alas, toggling any bit caused both to toggle. My question, how do I address subsequent bits in the circuits? Thanks in advance, John

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Digital IO is in the format of Word/Bit So, if you don't have IO at word position two then it's going to crash. The next consecutive IO point is 0/1 so I:0/1 and O:0/1 is the next available point in your example

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Thank you Sparky. Again, if I may impose, the format I:0/0, I:0/1, I:0/2, etc. continues up to the number of Inputs on the card (0/8 for a card with 8 inputs)? How is a second or third card addressed? Is it I:2/0, etc.; I:3/0 an so on? Thanks for your patience, John

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That is correct.

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Thanks, again! Eli.

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one of the best ways to learn how the addresses work is to explore the different "data table" files ... for example: double-click the little blue "output table" icon and follow the red arrow in the picture below ... this will take you to the "output image" table and show you all of the output bits ... now just click on any one of the bit/boxes and watch the address display change at the end of the arrow ... do this for a few minutes and you should start seeing a pattern develop ... note that you can click the pictures in the forum to make them larger and easier to see ... next try double-clicking the little blue "input table" icon and follow the other red arrow ... now you'll go to the "input image" table - and clicking on any one of the bit boxes will show you the address of the specific box you've got highlighted ... yes, there IS a pattern ... the straight blue lines show how a couple of the bit/boxes on the data tables correspond with the addresses shown in the ladder logic ... tip: try a right-click on an EMPTY area of the ladder logic window, then select Properties and then select Address Display from the popup menu ... experiment with different selections on this menu and notice how the format of the addresses can be changed to suit your own personal preferences ... in other words, if your screen isn't displaying the addresses in the same format as in the pictures, you can change the format around ... final tip: when you're writing a program, suppose that you've found a particular bit on the data table and you want to use that bit's address on something like an XIC instruction ... you can Click-and-Drag the bit from the data table and then Drop the address right into the ladder logic ... note: don't aim for the question mark over the instruction instead shoot for the little red target which will turn green when you've got the mouse close enough ... hope this helps ... good luck with your studies ... Edited by Ron Beaufort

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Ron, Awesome reply! Thanks!

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Not exactly. I was on a job site with a Microligix 1100 when I replied to your first question. The IO addresses for the PLC I was working with are as follows: I:0.0/0 thru I:0.0/9 These are the digital inputs that come on the PLC main chassis. Q:0.0/0 thru Q:0.0/5 These are the digital outputs that come on the PLC main chassis. Added cards: I:1.0 thru I:1.3 This is a 4 Channel Analog Input Card O:2/0 thru O:2.3 This is a 4 Channel Analog Output Card O:3.0 thru O:3.7 This is an 8 point Digital (relay) Output Card I:4.0/0 thru I:4.0/7 This is an 8 point Digital Input Card I could have put the two I's together and the two O's together or put the DI / DO combination ahead of the AI/AO combination or some variant. If I work with Control Logix, my typical application has the processor in Slot 0, an ENBT in Slot 1, An ENBT in Slot 2 if I have remote IO, blank otherwise, A 32pt DI card in Slot 3 and 4. A 16 pt. relay output card in Slot 5 and 6. Sometimes I'll leave a blank slot between DI / DO so the slot numbers will change. Following the DI/DO cards I install a 16 point analog input card in slot 7, 8, and 9. Slot 10 holds an 8 point analog output card. I've programmed 8 racks very similar to this setup this year. It's our standard pump station panel. If the need arises I may do something different but for the most part the IO is arranged Processor/Comm/Comm or space/DI/DI or space/DO/DO or space/AI/AI or space/AI or space/AO... unless I need to add a thermocouple card or RTD card. Those get placed between the AI and AO. I guess what I'm trying to say is that the designation for IO is rack / slot dependent. If I put a DI card in slot 9 then it's I:9. If I put it in slot 12 it's I:12. Edited by Michael Lloyd

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jagwinn, There's a good starter PLC online tutorial over at PLCS.net that you might want to check out. It's pretty generic, so it doesn't deal with addressing and high-level functions, but it's a good self paced review of the basics of how a PLC and ladder logic functions. Just another resource you may want to use! Jeremy

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Thanks for the direction, Jeremy! I will check it out. John

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