Modbus Ethernet communicat​ion problem

[websid]

Hello!

I have a problem with NI Modbus Library.

When I was testing the modbus Ethernet examples from the NI MB llb I discovered one funny case...

It is working with ordinary Ethernet cable, but does not work properly if I use only 4 wires of the cable (1,2,3 and 6 wires).

I guess it should be enough to use 4 wires.

So, the problem: I use one Slave and several Masters and the ethernet cable category 7. If I use 4 wires of the cable then I can use only one Master.

But when I try to connect another one Master then the Slave buzz and does not answer. I can not understand it...

If somebody knows the problem, answer me, plz

[Tim_S]

I have a problem with NI Modbus Library.

This sounds like a hardware issue and not the Modbus library.

I don't understand what you mean by using "only 4 wires of the cable". You need to have the cable wired to the spec or the cable won't work. Ran across one page that seems to show how it's done: CAT7 Cable Termination

Tim

[websid]

I use wires T+, T-, R+, R- (1,2,3 and 6 wires of the cable), but dont connect all 8 wires. Probably, I have to ckeck the cable connection once more... I guess NI MB LLB should work proparly.

[websid]

I have found the reason... The NI MB library does not work if PC has DNS address, but it connected to the local net without DNS server (i.e. without Internet).

[Tim_S]

I have found the reason... The NI MB library does not work if PC has DNS address, but it connected to the local net without DNS server (i.e. without Internet).

That would be an IP layer issue and not a library issue. The PC wouldn't be able to perform name to IP lookup nor would it be able to obtain a valid IP address.

Tim