Trouble getting Applicom Direct-Link and ControlLogix PLC to talk...

[trax]

Hi guys,

Quick disclaimer--I'm a major PLC newbie.

I'm trying to get a Windows PC to talk to an A-B ControlLogix 5561 PLC over Ethernet. Our goal is pretty simple--read some variables from a specific region in the PLC's memory. To do this, we're using the Woodhead / Applicom Direct-Link suite (http://www.woodhead.com/products/automation/communicationsoftware/), which allows you to plug a PC into a TCP/IP-based PLC network and read variables straight out of the PLC's memory. To be clear, we are not using one of Woodhead's interface cards--we're doing this through a typical store-bought Ethernet card.

I was able to set up the software so it can tell that the PLC's CPU card, located in slot 2, is alive. However, I've run into a snag--the Direct-Link suite addresses memory with a very goofy notation -- for example, "N5:1". The Direct-Link documentation seems to imply that this address should be intelligible to the PLC. However, when I've tried some different combinations (F128:2, for example, which should be valid according to the Direct-Link manual), the Direct-Link software reports that either the function (or the address, it's not clear which) is not supported.

Unfortunately, I'm a PLC newbie, so I wasn't quite sure what to look for to fix the issue. I tried looking for some hints about the memory layout through RSLogix. I can see how the variables/tags are mapped, but I didn't see anything that seemed to fit the goofy notation that I'm seeing in the Direct-Link software.

Can anyone suggest how I might be able to fix this problem?

Thanks!

 

[CroCop]

You're barking up a wrong tree.
While the ControlLogix will support the N7:0 style addressing, most programmers don't use it. CLX supports tag based addressing, with names like My_Tank_Level or High_Limit_Level, etc.

Do you have a manual or a link to a manual of the Direct-Link examples?

 

[trax]

Sure do... first link on this page:

http://www.woodhead.com/support/onlinesupport/applicom_direct_link_sst/manuals/

 

[CroCop]

OK, to the crux of the issue:
On page #10:

Logix5000 messaging can only be used via OPC and DDE (WHDDE) interface.​

​

This means you'll need to have an OPC or DDE server to get to the Logix platforms. I like Kepware servers, they have worked extremely well for me in my applications.​

 

[trax]

Thanks CroCop, that's definitely helpful! I'm unfamiliar with OPC, so I'll have to read up on that.

Now for my second question...
We don't always have customer PLCs at the office to use for testing. Ideally, I'd like to be able to test the Applicom function calls without actually having the PLC present. Is there a way to do this? It seems like when I have no PLC hardware connected, any function calls other than the init/shutdown calls return error codes. I have a support ticket open with Molex about this issue.

I understand that without the PLC hardware, any variable requests would probably come back as 0's... which is fine. The main thing we're trying to do is ensure that we're performing function calls in the correct sequence. That way when we do get access to a PLC, we only have to worry about the location of variables, not whether or not we're using the API correctly.

Thanks!