Connections - foxboro / Re: [foxboro] Nodebus Bandwith

Re: [foxboro] Nodebus Bandwith / Connections

From: "Johnson, Alex (Foxboro)" <ajohnson@xxxxxxxxxxx>
To: foxboro@xxxxxxxxxxxxx
Date: Fri, 21 Jun 2002 04:17:21 -0400
Long story short: It is always more efficient to send fewer data items, but
it doesn't always matter



Long story:


The CP optimizes its OM access to other CPs. By that I mean that it will
create a list and add points to it until it thinks the list is long enough.
(The actual limit on an OM list 255 points, but I think the CP limits its
lists to 150.)


The CP also sends data between stations only when it changes by enough to be
interesting. For floating point numbers, you set the delta. Integers and
Booleans are sent on each change.


Each monitored variable (each name on the list) that reports a change uses 8
bytes (2 for index, 4 value, 2 status). The size of the value is the same
for all data types.


Finally, the OM sends a heart beat on the list every two seconds if no data
has been sent. This lets the other station know that the source is alive.


So, unless you have a truly large numbers of these connections, I doubt that
you will notice a difference with either implementation.


Which brings me back to:


It is always more efficient to send fewer data items, but it doesn't always
matter



Regards,

Alex Johnson
Invensys
10707 Haddington
Houston, TX 77063
713.722.2859 (office)
713.722.2700 (switchboard)
713.932.0222 (fax)
ajohnson@xxxxxxxxxxx <mailto:ajohnson@xxxxxxxxxxx> 
Come to the Invensys Showcase: http://www.invensysshowcase.com/
<http://www.invensysshowcase.com/> 


        -----Original Message-----
        From:   John Miller [SMTP:JMILLER@xxxxxxxxxxxxxxxx]
        Sent:   Thursday, June 20, 2002 5:19 PM
        To:     foxboro@xxxxxxxxxxxxx
        Subject:        [foxboro] Nodebus Bandwith / Connections


        I'm trying to do some planning for a future job and I was wondering
which of
        my options put the least demand on the system.  The first option
would be to
        use a LOGIC block to check the status of six binary inputs, run an
operation
        and then output the result in a form where .BO1, .BO2, and .BO3
would equal
        one to indicate the result.  All three binary outputs would be read
by a
        CALC block in another CP.

        The second option would be to take the same six binary inputs, run a
        slightly different program and output the result to either the LOGIC
block's
        long integer output.  The result would be a number 0-3 indicating
the result
        and would be picked up by a CALC block in another CP.  The resulting
number,
        0-3, would equate to binary outputs .BO1 - .BO3 in the previous
option.

        The third option would be to use .BO1 and .BO2 to output the
resultant 0-3
        encoded in binary.  That result would then be picked up by a CALC
block in
        another CP.

        This same type of operation may get repeated several times in many
        compounds, which is why this might eventually become an issue.  I
guess the
        question boils down to whether it's more efficient to transfer the
three
        binaries to another CP or send the data as a long integer or encode
the
        information in two binary outputs?

        Thanks,
        John Miller
        Hunt Refining Company
        1855 Fairlawn Road
        Tuscaloosa, AL 35401
        205.391.3345
        jmiller@xxxxxxxxxxxxxxxx
         
         
        
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Re: [foxboro] Nodebus Bandwith / Connections

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