PLC5 - cross reference shows different tag?

[hunter44102]

All - I don't know much about PLC5, I am more from ControlLogix.

Can someone answer this:

So I am looking at a N262:10 tag with offset 2 (N262:12) which has a value of 100.

When I right click on the Offset 2 (N262:12) to do a cross reference, why does the cross reference report show N262:18 as the top result? What are these results when it doesn't show N262:12 anywhere?

thanks

[joseph_e2]

I don't have a license for RSLogix 5 any more, but I remember this functionality being a lot like RSLogix 500. Do you see that value changing?

In 500, when you go to the cross reference, it shows you how that memory location is used. If you open it up and don't see N262:12 directly, scroll up to lower addresses and look for a COP or FLL that has a LEN parameter that would extend to or past the address you're looking for. Look also for BTR (block transfer read) instructions that use that address or a lower address that's nearby. If you're in the data file, click the "Usage" button and it'll show an "X" on addresses that are used in the PLC. In RSLogix 500, it will show that address as used if it's within the range of a COP instruction (for example). If you open the cross-reference, though, you may have to scroll up to see the COP instruction listed under a previous address if N262:12 isn't used in the code directly.


Another possibility is that it's being written to by an HMI or by a MSG instruction from another PLC.


By the way, that's not really a tag with an offset. It's just a memory location. In the PLC5 world, storage memory is arranged in files (file number 262 in your case) with individual elements. This one is "N", which is intended for storing 16-bit 2's complement signed integers. You can get to individual bits in each register as well. So N262:12 is just a 16-bit integer register.

[Operaghost]

Keep in mind, what you are looking at is a report. It shows every address in the controller cross-referenced to it's location in logic. If that particular address is not located in the logic, it will show you the next closest address. That would seem to indicate that this address is not used in the logic. As joseph_e2 mentioned, the value you are seeing in that address may be coming from an HMI or another device on the network.

Another option when you are looking at the Data File is to select "Usage". It will show you what addresses are being used. It doesn't give you the detail of the XREF report, but it helps you identify addresses that are available for use.

OG

[kekrahulik]

Cross reference returns a report. So you will have to realize that what you are looking for isn't used because it's not in the report.

In PLC5 or PLC500 the "Find All" is often more helpful/friendly than the "cross reference". If the address is not used, "Find All" will return "xxx was not found".

Operaghost's comment about "usage" is also very helpful when looking at datatables.

Cross Reference is needed if you are looking (for instance) at a timer done bit and want to find the timer, because "Find All" will only find the specific done bit usage.