CLX I/O Configuration: "Assembly Instance" ??

What the heck is "Assembly Instance " ? I see that I have to fill it in when using a HiProm Profibus gateway.

I don't see any AB help about it. And searching the 'net doesn't reveal anything relevant.

On a side note: for this profibus-PA device, it needs a REAL tag (for the Process Variable) , but only DINTS show up when defining the communications format and in the I/O controller tags when the Gateway is defined. Is there a way to coerse a DINT to a REAL?

The required assembly instance values should be provided by the module's manufacturer. They are the 'Raw' way of telling the Logix processor how to format communications to the module. With AB or actual defined modules with full EDS Files, most of that is hidden behind the scenes.

As far a data formats go, depending on endian-ness (Byte Ordering), you might just be able to do a block copy (COP) from the DINT array to an array of REALS (of the same size). Both datatypes are 32 bits, and COP doesn't care about the source and destination data as long as there is room in the destination array.

If you have an endianness problem, then you will either have to try to get the gateway to 'play nice', or you will have to byte swap the pieces of each 32 bit DINT until you get the right endian format to copy to a REAL.

rdrast said:

The required assembly instance values should be provided by the module's manufacturer.

Click to expand...

But which manufacturer ? AB CLX, the profibus gateway or the profibus instrument ? The only place I see it called out is a screen shot by the profibus gateway company.

There are 3 entries: Input, Output & Configuration.

Thanks for the COP hint, I'll try that.

theDave2 said:

But which manufacturer ? AB CLX, the profibus gateway or the profibus instrument ? The only place I see it called out is a screen shot by the profibus gateway company.

There are 3 entries: Input, Output & Configuration.

Thanks for the COP hint, I'll try that.

Click to expand...

The Profibus gateway company. The instruments have nothing to do with the interface to the Logix backplane, and the CLX only needs the assembly instances (which generally correspond to the ":I, :O, and :C" entries in the tag table) in order to talk to the module.

"Assembly Instance" is the pointer to a specific memory location within a device that supports CIP. These numbers are device specific. Only device manufacturer can provide this.

Contr_Conn said:

"Assembly Instance" is the pointer to a specific memory location within a device that supports CIP. These numbers are device specific. Only device manufacturer can provide this.

Click to expand...

One has to admit that the term iself - "Assembly instance" - is very counterintuitive and confusing.

I agree that "Assembly Instance" is not very descriptive for electrical engineers who typically program PLCs, but looks like most of CIP specification written by "C" programmers and "object oriented" thinking is normal for these guys.

Contr_Conn said:

I agree that "Assembly Instance" is not very descriptive for electrical engineers who typically program PLCs, but looks like most of CIP specification written by "C" programmers and "object oriented" thinking is normal for these guys.

Click to expand...

I do 'C', I do 'OOPS', I never heard of it before now.

BTW, I did use a COP and that did 1/2 the trick. The other 1/2 was finding out that the PIT display reads out in PSI but the Profibus was sending the pressure in BAR.

Dave:
I found some examples at: http://www.hiprom.com/Pages/Products/1788_Range/1788HP-EN2PA/web/1788HP-EN2PA.htm

Contr_Conn said:

I agree that "Assembly Instance" is not very descriptive for electrical engineers who typically program PLCs, but looks like most of CIP specification written by "C" programmers and "object oriented" thinking is normal for these guys.

Click to expand...

Tsk Tsk!
C is definately not an OO design language, that's what C++ is for, which is actually a similar, but very separate language (Not just an extension to C, in other words).