ControlLogix String type

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1

Hey,

I’m trying trying to receive a string from a ControlLogix PLC. The string will contain an ID code and a material description. When I browse it in the SQL OPC browser all I am getting is folders with the array. Am I doing something wrong? How do I get it to come in as a string and record as a string?

ANy help is greatly appreciated.

2

JoshMan,

I have had to deal with something just like this recently. There are special addressing rules for your OPC server that dictate how to read strings. I think that in RSLinx the format is [TopicName]address,SC(length).

For example, if you have a 15 character string starting at n25:4 and the Topic name is “PLC1”, you would use:[PLC1]n25:4,SC15 as your item address. This may not be the right format for a ControlLogix processor, but the correct format will be in the OPC help file.

3

Thanks, but that didn’t work.
There is no memory location like that with Control Logix. PLus its an array, so would it also need the .DATA[0].SC(length)?

4

What OPC server are you using?

EDIT:

From the RSLinx help files:

[quote]ControlLogix 5550: addressing syntax
The format for solicited DDE/OPC items for the Logix 5550 processor is as follows:

For globally-scoped tags, use your user-defined tag names as the item names.

For program-scoped tags, use the format of Program:ProgramName.TagName for the item names. For example, if the program name is Power and tag is Output, the format for the item is Program:Power.Output.

The addressing syntax for a ControlLogix String UDT is STRING.DATA,SC# (where # is the number of characters). For example, use STRING.DATA,SC10 to read the first ten characters of STRING.DATA.

The addressing syntax for ControlLogix I/O bits is [Local|Remote]::[I|O].Data/bit. For example: Local:2:O.Data/1.
[/quote]

5

Hey Thanks

That worked