Why is there sometimes a connection delay when connecting a cFP processor?

[dj143]

I'm connecting a cFP-2110 processor to the Ethernet port of a host computer.  When I give the Connect command it often promptly connects but sometimes it doesn't.  When it doesn't connect I'll either get the "Access Denied" or "Connect Failed" conflict message.  If I wait long enough (i.e. 30 to 60 seconds it seems) it will eventually connect.  I read somewhere that there is a time-out function internal to the processor that is required for it to recognize it has been disconnected. 

Could someone explain the concept behind this?  Is there an appropriate way to shorten the connection delay?  I need to prepare an operator's manual for the end user and would like to better understand how it works and what to expect.

Thanks,

Dave J.

[Abhinav T]

Dave,

Thank you for posting to the National Instruments Discussion Forums.

The time-out function you mentioned is called the watchdog timer and it allows you to detect periods of network inactivity and have the FieldPoint controller react in a user defined way. You can find more information on this functionality from the following link:

FieldPoint Watchdog Timer

This watchdog timer functionality only helps you on the controller side. Your issue seems to be more related to the communication between the host machine and controller. The following article gives a good starting point to understanding how you can connect to your FieldPoint module:

Unable to Locate an Ethernet FieldPoint Network Module in MAX (or FieldPoint Explorer) in Windows XP

As I had mentioned earlier, this maybe a communication issue between your controller and host machine. How are you connected to your FieldPoint controller? Do you have a cross-over cable or is there a router in the middle? Is the controller recognized in MAX?

Hope this helps!

[dj143]

Hi Abhinav,

Yes MAX recoginzes the processor and things work great once connected.  A crossover cable is used and there is no network involved.  The application is relatively simple.  All the cFP does is receive data through an RS232 port and a 4-20mA signal from a sensor.  The only module in the back plane is a cFP-AI-100.  The system then processes the data and sends it out through another RS232 port.  The system is intended to be a stand alone device during normal use.  The only time a host is involved is for system configuration.  For example, the single 4-20 mA signal needs to be scaled to wanted units.  The host computer will normally be a laptop that is provided by the end user.  We will provide an executable program that the end user will install on their laptop.

I've used LabVIEW sinse version 6i.  However, this is my first RT project; so the Ethernet usage and addressing issues are new to me.  So far I'm very pleased with the results and am making good progress with the project.  I'll look into the references you mentioned.

What is the appropriate options for setting up the IP addressing  when we will not know what the computer (i.e. address) will be in the field?

Thank you for your response,

Dave

[Abhinav T]

Dave,

When you use a cross over cable you essentially assign a static IP address for both your host computer and the FieldPoint target. Your host computer should not be using DHCP to assign IP addresses. Here is another link you can use to setup the Fieldpoint controller using a cross over cable:

Connecting a Fieldpoint Controller Directly to an Ethernet Card

Hope this helps!