[Visual-devel] Re: [MAT-devel] visual PLC drivers

[Thomas H. <Tho...@we...>]

mat...@li... schrieb am 12.02.04 14:57:28:

Hello,

>Jiri:
> >as far as visual is concerned, what's the situation with MatPLC taking
> >advantage of visual's PLC drivers? Can that be done with the existing
> > code,

>Thomas Hergenhahn:
>> I don't know whether this can be done with the existing code in mat as, I
>> did not download recent code for quite a while. But I also think this is
>> not the way to go: The drivers are shared objects, but they heavily rely on
>> VISUAL's "infrastructure".

>Right. It just seems a duplication to have separate drivers in the two 
>projects...

>> sequences) to and from the PLCs and to close the connection.

>I think we have libnodave on our to-do list, but nobody's got around to it 
>yet. (Unless you'd be willing to interface it to the MatPLC?)
Ok, I consider this.

>> See also my remarks on this subject in:
>> http://www.control.com/1026183428/index_html

>Yeah, that whole thread is interesting. Getting a unified driver interface 
>would be very good.

>> I should like to suggest that you might use these functions to interface
>> with matPLC. For VISUAL, I plan to modify PLC drivers in a way that they
>> rely on library routines providing above described functionalty.
>> This means also that I'm prepared to provide the protocols for the other
>> PLC families supported by VISUAL in similar libraries. My problem is that I
>> do not have different PLCs from each manufacturer to testwith.

>The other possibility would be to migrate all the drivers to one project or 
>the other, and interface the two together. 
I don't think so. What I tried to say in the above mentioned thread on control.com and what I tried 
in designing the interface of libnodave is to design it for general purpose useful to many more 
projects.
>For instance, if the drivers were 
>migrated to the MatPLC, the VISUAL server would link against the matplc 
>library instead of loading the PLC drivers.
In VISUAL it is not THE library, but shared objects for each PLC type, because most users will not 
need more than one while the total number of supported PLCs may (hopefully) reach hundreds 
(Seeing the lists of other SCADA vendors...).

>(The MatPLC points are named rather than having a dev/subdev/area/offset 
>structure,
This structure doesn't reflect VISUAL's side, but is meant as a superset of the supported PLC's 
addressing scheme. In addition to these items, there are an area number and a transport method.

"device" one of multiple physical units on a common interface
GE Fanuc: SNP address
Allen Bradley: Data Highway node number
Siemens: MPI address
modBus: not used, possibly IP address

"Subdevice" would address a part(rack,slot) in the device.
Not yet used ?
modBus: modBus unit ID

"Area " addresses a type of memory where addresse begin from start:
GE Fanuc: M,R,AI,AQ etc. memory areas
Allen Bradley: Area type is (N,F,...) but is not really evaluated.
Siemens: Data , Flags, or Input/Output,
modBus: not used

"Area number"
GE Fanuc: not used
Allen Bradley: File number
Siemens: Data block number in case of data.
modBus: not used

"Transport method"
GE Fanuc: "R" for read or "W" for write
Allen Bradley: A valid combination of CMD and FNC codes, e.g. "0xF 0xA2"
Siemens: "R" for read or "W" for write.
modBus:  codes 3,4,15,16 if I remember right. Ok, they determine areas here also (registers, input 
registers) but its easier like this, because the library doesn't need to know about them.

> but otherwise it's fairly similar to your proposal. There's a 
>couple of extra functions to ensure that a bunch of values all come from the 
>same scan and to let the library limit your scan rate, but that's it. All up, 
>it's seven functions to call.)

>Possibility three is the DAIS thing, which is pretty much the equivalent of 
>OPC, but it's a bit heavy-weight for our purposes. Eventually we'll need DAIS 
>anyway, but for communicating over the network, not for local interface.
I don't know that.

Thomas


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