Try as I might......

Ok, this has all of the elements of a stupid question but try as I might, I have not been able find the answer. For example,in an AB 1400, if I set up for an input from I:0/0 and it goes true, is bit I:0.0/0 true? If I set up for I:0.0/1 and I:0/0 goes true does bit 1 go true. I'm having a difficult time understanding addressing as you may see. Thanks in advance for any help.

right-click on an EMPTY area of the ladder display ... then go to the "Address Display" tab ... play around with the different settings and watch how they affect the format of the addresses shown on the screen ... this will probably answer the questions you've asked ...

Thanks Ron. I'm at home trying to upgrade my limited self taught knowledge and I don't have access to the work computer.(We have RsLogix and they only paid for one license so I can't have it at home)

I:0.0/0

I = "Input" - I'm gussing you figured that part out

:0 = "Slot 0" - Again I think you have this

.0 = the first ("zeroeth") word from that slot. Some input modules have more than one word associated with them. This part can be left out, in which case word zero is assumed. Some instructions though may insist on the word part.

/0 = the zeroeth bit of the word. Without the "/x" section the reference is to the whole word. In some cases with a multi word item the bit reference can be set such that the word and the bit are shown. An alternative method is to treat all the words as a continous series of bits and show the number of the bit starting from the beginning without a word reference. (0 - 15 in first word, 16-31 in second word etc) (I get horribly confused by that and don't use it.)

But you refer to I:0.0 going "true". A complete word holds 16 bits, usually interpreted as a number. It usually is not interpreted as "true" or "not true". That type of designation is usually reserved for the bit level.

I haven't worked with the 1400, but have worked with the 1000s, 1200s
Assuming you only have 16 (or less) inputs
changing I:0/0 will change only I:0.0/0
Changing I:0/1 will change only I:0.0/1.
Basically both I:0/0.0 and I:0/0 are the same address.
I:0.0/0 = I:0/0
I:0.0/1 = I:0/1

I don't want to get to deep into how the addresses break down but I will say that:
The first '0' in I:0/0.0 specifies the card or in your case the 1400 itself.
The second '0' in I:0/0.0 specifies the word....or which group of inputs to look at, 0 specifies the 1st 16 inputs, a '1' would specify the second group of 16 inputs. For instance if you wanted to look at input 24, you would be looking at bit I:0.1/7 (or the 7th input on the second set of 16 inputs) Ii know it's a bit confusing.

An easy way to see it is to change the input while looking at the input data table. This might help you see the relationship.

Hope that helps




The first '0' in I:0.0 is specifying the 1400. The second '0' is specifying the word address or telling you it's one of the first 16 inputs (0-15)

Thanks Bernie. The part I'm really not getting is when I put + 24VDC on IN0, what do I get true logically: I:0.0/0 or I:0/0. If either is true depending on the way the input instruction is set up, what would be the advantage to one or the other.
(I know this is like trying to teach a monkey how to drive but my company is sitting on the training dollars so I'm kind of scratching around for knowledge!)

Mbeavers, Thanks very much....I'm beginnig to see light at the end of the tunnel.

We have all been there at one time or another...soon you'll be the expert

piece of advise an excellent training aid is Jack Hughes book

http://claymore.engineer.gvsu.edu/~jackh/books/plcs/pdf/

nice thing about this one is that its written for the AB format

the link includes his various revisions so get the 5_1 version

For the purpose of that single bit the two addressing forms are equivalent. The first emphasizes that this is bit zero from the first word (as opposed to other possible words this input might have). The second for leaves off the word specification so word zero is assumed.

peterc49 said:

Thanks Ron. I'm at home trying to upgrade my limited self taught knowledge and I don't have access to the work computer.(We have RsLogix and they only paid for one license so I can't have it at home)

Click to expand...

You know you can download the 10 point version of RSlogix programming software to your home computer.
It might be fun to play around with.
Rockwell instructions here.
Good Luck

I recommend
1. Getting all of Melores info available on this web page
2. Giving up on you being both student and instructor at home
3. See if you can get a class on PLC in your community. Check with community college or local IBEW or if you state has continuing ed hours their listing of classes and instructors.

That is what I did - worked well - went the community college route. They had more versions of PLCs computers all set up and ready to go. Good instructor on top of all that.

Dan Bentler