SLC-500 Input Registers

Hi,

I have an existing system reading N and B registers correctly. When I try to access Input registers I receive STS F0 b errors which I believe are access denied errors.

Two questions.

Can I enable reads for Input registers in the PLC using RSLogix500?

or

Whats the easiest way to do a bit-copy from I registers to B registers? lets say my data sits in I:10/1 and I want to place that in B3:78/1 so I can read it.

Hello,

You do not state the software you are using to read the data.

Yes it is possible to read the input registers of some SLC CPU.

From our help file: Fixed SLC, SLC 5/01 and 5/02 do not support digital input and output data table access.

Assuming the SLC is not a 01 or 02 then the read is best performed a card at a time.

From our help file: Note: When configuring reads if the file type is input or output be aware that setting the count greater than the number of words the card supports, may or may not return data (a successful read). In some cases the PLC will return the data for the selected card (slot) and additional cards (slots) up to the count value.

It is a SLC 5/04. An industrial control system is doing the reads.

I've known of some IO Server programs that had known bugs with accessing SLC Input or Output tables. That said, I wouldn't recommend doing it anyway. I prefer to avoid having any IO Server directly address real I/O tables in any PLC as a general rule.

If you only need to read the status of a few Input points, then you could write simple ladder logic to have the Input of interest addressed to an XIC contact instruction which operates an OTE coil addressed to a bit in the B3 table. Then read the B3 bit with your HMI rather than reading the actual Input point.

If you need to monitor the status of multiple Input points, then you could use the COP (copy) instruction to move an entire word (or words) of Input data to a B3 word (or words). You should not use the MOV (move) instruction when you are interested in the bit pattern, rather than the numerical value of the data being transferred from one word to another.

Hello,

> It is a SLC 5/04.

OK. Then it is possible to read the inputs without error. PeakHMI can read the inputs without error.

friedmators said:

Whats the easiest way to do a bit-copy from I registers to B registers? lets say my data sits in I:10/1 and I want to place that in B3:78/1 so I can read it.

Click to expand...

Use the COP instruction. Depending on your I/O layout, a single instruction could do everything. Let's say you have 5 input cards in slots 1-5, addresses I:1/0-15, 2/0-15...5/0-15

COP copies everything by word, so you'll have to reserve five B words for the data, so Let's say B11:1, B11:2, B11:3, B11:4, and B11:5

So then all you do is make a single unconditional rung with a single COP instruction. Set your Source parameter to I:x (where x is the slot number of the first input card in the group), set your Dest parameter to B11:1 (or whichever address you want the input cards to begin mapping to), and set your length to the number of cards you want to copy over, which is 5 in this example. It will then copy I:1/0-15 to B11:1/0-15, I:2/0-15 to B11:2/0-15, and so on.

Whats the easiest way to do a bit-copy from I registers to B registers? lets say my data sits in I:10/1 and I want to place that in B3:78/1 so I can read it.

Click to expand...

Yes like FactoryTalk said, use one copy instruction.

But if you cannot read the "I" data directly, then you probably can't read the B3 data either.

Lancie1 said:

Yes like FactoryTalk said, use one copy instruction.

But if you cannot read the "I" data directly, then you probably can't read the B3 data either.

Click to expand...

Why would you say that Lancie? According to the top post, B3 reads are already working properly.

Experience is the only reason that I said it.

We don't know anything about the "industrial control system" the OP is using, but we do know that some drivers don't correctly read the I and O data tables of PLC/SLC/MicroLogix controllers.

The easy answer is to use the COP instruction to move the Input data tables to a B or N file, and read that. That's the way I have always done it.

Ken Roach said:

We don't know anything about the "industrial control system" the OP is using, but we do know that some drivers don't correctly read the I and O data tables of PLC/SLC/MicroLogix controllers.

Click to expand...

I can't remember exactly but the Standard Panelview will either not read or not write to the I and O data tables over Ethernet/IP.

Copying the I and O tables to something else is good practice anyway.