ControlLogix String type



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.




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.



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)?



What OPC server are you using?


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.



Hey Thanks

That worked