Can I have 2 gpib-enet/100 devices on the same GPIB Bus?

[JoeK]

Our project requires that there is no single point of failure, and this applies also to our GPIB-ENET/100 gateways. What would be the best way to have high availability with regards to the GPIB-ENET/100? I've tried having 2 GPIB-ENET/100 devices on the same GPIB bus, but that seems to cause major problems when they both try to talk at once.
Please help!
Thanks!
Joe Kralicky

[AaronK]

Hi Joe,

You should be able to do this without too much hassle. You will have to make one look like an instrument by disabling the system controller option on it. You can only have one system controller at a time so if you had both ENET's on the same bus, that would be the problem. Basically what you can do is make on ENET do all the work. If you detect that things are not working correctly, shut that one down by turning off its system controller flag and then enable system controller on the other instrument.

Hope this helps out Joe!

Best Regards,
Aaron K.
Application Engineer
National Instruments

[JoeK]

Hi Aaron,
Thanks for your response! Late last night I tried the following very similar to what you describe and it seems to work. Let me know if there's something that doesn't seem right:
1. I configured my 2 ENETs to BOTH *not* be system controller. I also made the primary addres on one of them to not be 0 so as not to conflict with the other.
2. When communications start (not knowing for sure which ENET will get hit first), I always get the first command in error (ESAC), then I do 'ibrsc', and retry the command.
3. If I turn off the active enet, my program detects this by my gpib communication thread hanging - since any gpib command will not return with an error if we lose comms to the ENET (which I guess is a known bug).
4. I then switch to my b
ackup computer, and talk to the other enet. I still get the ESAC and do
'ibrsc'.

I don't ever do 'ibrsc 0' but it seems to be working.

Sound ok?
Thanks again!
JoeK

[AaronK]

Hi Joe,
I like how your scheme is set up. The only question I have is why not make the ENET box that is set to address 0 to be by default the system controller and have the other box set to be the device. Then only handle broken comm links when they come up?

Other than that it sounds like a really cool project. I like the idea of redundant communication. Very cool! 🙂

Aaron K.
Application Engineer
National Instruments