can bits be inputs

lets say i'm looking at a bit(B3)in a PLC 500 project. the bit is B3/16:1, which is the frst bit in a rung. I do a "find all" on that bit and the only other thing that shows up is the output instruction(OTE) for that bit, B3/16:1.when i go to the data table and look at the usage i see an "X" for the input. (i guess). My question is can an input into the PLC be a bit input? if the bit is the frist instruction in a rung and it only has one output to the (ote) instruction. how can i find what makes that bit true in the first place.

Continue to analyse the rung which has the OTE for that bit. What conditions make it true?

technically speaking, a BIT is a BOX that can hold either a ONE or a ZERO ...

now then, how the ONE or the ZERO gets into the box is another story ...

also, there is no limit on how many times the PLC processor is allowed to "look in the bit/box" for a ONE or a ZERO ...

and to answer a specific question ... an "X" on the "Usage" feature table just means that the specific address is being used/mentioned somewhere in your Ladder Logic program ...

finally, some friendly advice ... you need to be a lot more careful with your typing ... the mistakes that you're making with the addresses you've listed are going to cost you a lot of time and trouble in the long run ...

To expand on what has already been said, and to specifically answer your question.....

The PLC contains numbered data-files that are used for storage of specific types of data...

O(0) Outputs *
I(1) Inputs *
S(2) Status *
B3 Binary (Ron's Bit/Boxes)
T4 Timers
C5 Counters
R6 Controls
N7 Integers
F8 Floating points

etc.

(* O, I, and S file numbers are NOT required, and you do not need to specify them)

Data from the O file is automatically sent out to Output modules in the system.

Data in the I file is automatically collected from your Input modules.

So the answer to your question "can an input into the PLC be a bit input", is No! Inputs to the PLC go into the I data-file.

B3, N7, F8 are files for internal storage of data.

Now your code can look at (read) data in any file, and it can change the contents of (write) data to any file.

Instructions on the left of a rung of code are called "conditional" instructions, they are looking at data and deciding whether the instruction/data combination is true or false.

Instructions on the right-hand end of a rung are called "output" instructions (nothing to do with physical Outputs), and the PLC actions these depending on whether the rung is true or false.

The bit address you are looking at in your post, B3:16/1, is an internal storage bit, and will usually have one (or more) OTE, OTU, or OTL instructions to write the value 0 or 1.

Then other code will want to know whether its a 0 (XIO or -|/|-), or whether its a 1, (XIC or -| |-)

More useful than going to the data-table and looking at usage, is to use the Cross-Reference facility, which will show where individual addresses are used in the code.

This will tell you where B3:16/1 is being turned on, or off.

Very very helpful "daba" and thanks for the advice "Ron". Here are two screen shots. I need help on finding out where I can go to find out what makes these XIC bits(B3's)true..

Is there an HMI associated with this PLC? N11:0/7 in the first screenshot (and some MOV blocks in the 2nd shot) could be aimed to a PanelView. If this is the case, the B3 bit could come from the PV as well. You can get bit info (BX:X/X) and integer info (NX:X/X) both from HMIs and you'll need to look into that program for the origin of the data.

Also, if you want to see what the STATE/VALUE of a bit/integer is, click on the "Data File" button on the bottom of the Data Table.

showshocka said:

Very very helpful "daba" and thanks for the advice "Ron". Here are two screen shots. I need help on finding out where I can go to find out what makes these XIC bits(B3's)true..

Click to expand...

What makes those bits go true is in File 2 Rung 50 and File 2 Rung 109. How about screen shots of those rungs?

Block copies on "I" files can be done, too. You might not find the specific "B" bit you're looking for, but look for a COPy of "I" files to "B" files.

showshocka

I don't know if its just a figure of speech, but you again ask " I need help on finding out where I can go to find out what makes these XIC bits(B3's)true..".

Let me put it this way - there is no such thing as an "XIC bit", or an "OTE bit". The bit is a bit in memory that can be looked at with XIC or XIO conditional instructions, or can be written to in your code with OTE, OTL, or OTU output instructions.

As already said, sometimes these bits have NO output instructions driving them on or off. Sometimes the whole word B3:5, or the file B3 may be written to, either in the code or from an HMI etc.

From your screenshot, you did a "Search" for the address (output in the bottom window). This shows you where the OTE is that drives this bit (File 2, Rung 50). But remember I said...

daba said:

......More useful than going to the data-table and looking at usage, is to use the Cross-Reference facility, which will show where individual addresses are used in the code.....

Click to expand...

Cross-reference is faster than searching, and will also pick up places where the word (B3:5), or the file (B3) are written to.

HTH

Greetings daba ...

I sincerely don't want this to become an argument – or even a debate ... I simply don't want to be misunderstood on this particular subject ...

the list that you made earlier (quoted below) doesn't accurately reflect what I've been saying ...

O(0) Outputs *
I(1) Inputs *
S(2) Status *
B3 Binary (Ron's Bit/Boxes)
T4 Timers
C5 Counters
R6 Controls
N7 Integers
F8 Floating points

Click to expand...

actually the following would be more accurate ...

O(0) Outputs * (Ron's Bit/Boxes)
I(1) Inputs * (Ron's Bit/Boxes)
S(2) Status * (Ron's Bit/Boxes)
B3 Binary (Ron's Bit/Boxes)
T4 Timers (Ron's Bit/Boxes – 48 bits per timer)
C5 Counters (Ron's Bit/Boxes – 48 bits per counter)
R6 Controls (Ron's Bit/Boxes – 48 bits per control)
N7 Integers (Ron's Bit/Boxes – 16 bits per integer location)
F8 Floating points (Ron's Bit/Boxes – 32 bits per floating point location)


(please correct me if I'm wrong) but apparently you seem to be defining a "bit" ONLY as a storage location which is assigned to the B (Binary) data type ... in my opinion, that's not correct ... my definition of a "bit" is ANY storage location which can hold a status of only a ONE or a ZERO ...

then going further and using that definition,

(a) a "bit/box" can be used to store a signal coming IN FROM the outside world ... or ...

(b) a "bit/box" can be used to store a signal to be sent OUT TO the outside world ... or ...

(c) a "bit/box" can be used to store a signal which has NO connection with the outside world ...

so ... considering the statement that you made earlier:

So the answer to your question "can an input into the PLC be a bit input", is No! Inputs to the PLC go into the I data-file.

Click to expand...

I would express the underlying thought this way:

Each input to the PLC goes into the Input data-file – and gets stored in a bit/box which has an address starting with the letter "I" ...

as I said earlier, I really don't want this to become an argument or even a debate ... but I can say with absolute assurance that lacking an accurate definition of the three-letter word "bit" is one of the biggest stumbling blocks for technicians trying to fully understand PLCs ...

for anyone who's interested in digging deeper into this subject, you'll find more information in the videos I have posted on YouTube (links are provided on the "Sample Lessons" page of my website) ... naturally you can expect to get more out of the lessons by watching all eleven of them IN NUMBER ORDER – but if you're short on time, Lesson #5 covers the definition of a "bit" according to the way I teach it ...

Noted Ron, just trying to keep it simple for the OP at this point.....

WOW, it just hit me like a ton of bricks!!!!! maybe i was wording it wrong.(which i probably was) I'm little new to the depth of this PLC world but, i see now that the command bits i was asking about such as B3:0/12 are controlled from the OTE B3:0/12 which, it is controlled from a logic 1 sequence, everything being a logic 1 path back left making the OTE B3:0/12 a logic 1 out,and so on...WOOOW thanks a lot guys!

I rather thought that was the case, showshocka, you not seeing that the B3 bit is just a memory location that can both be read, with XICs and XIOs, and written to, with OTEa, OTLs, and OTUs.

It's the same for any other data-table address, of course, whatever the data-type (although you won't be using the "bit" instructions, you'll be using MOVs and Math instructions etc.

You can even write to, (if you feel a need to do so), the Input image table (I) with code, but be aware that the data in there will get overwritten by new data from the Input modules prior to the next scan of the code.