DH+ terminating resistor question

[detrimental1]

I am working with a simple PLC to HMI to HMI DH+ network that has a Graceport programming terminal at the end of the blue hose on the DH+ network. Should the terminating resistor be on the programming port, or on the last HMI?

 

[Ken Roach]

The safe thing is to make the physically last device the location for the terminating resistor.

The DH+ lead to whatever connects to the Graceport (probably a 1784-PCMK or 1784-U2DHP) will be a short spur, but that's normal. If the cable to the Graceport was also a spur, that might make the overall length too much.

DH+ is amazingly forgiving of wiring variations, but it doesn't cost anything to do it by the book.

 

[detrimental1]

I would describe the wiring of PLC to HMI to HMI to program port as a daisy chain, no?
Just to go further, I have found that the DH+ network is communicating at 57.6 kbaud, but currently has an 82 ohm resistor at the PLC end and no resistor at the program port, which is where a laptop with a pcmkb card in it is sometimes hooked up. There has been a history of communication glitches at this equipment, and an inability to connect this machine to a larger DH+ network (also 57.6K)that allows for programming at a nice desktop set up. I hear that every time they tried to hook up this machine, it would always take down the whole network. Thanks for your feedback and any further comments associated with this reply.

 

[Mickey]

communicating at 57.6 kbaud, but currently has an 82 ohm resistor

At that baud rate the resistors should be 150 ohms.

 

[detrimental1]

Mickey,
Yes, this is definately wrong, so I think that is why there have been lots of issues with this control system causing momentary warnings about comm problems. I believ I need 150 ohm at PLC and at the Graceport (bitter end of DH+ network).

I have just installed both and anxious to see if I get any more momentary comm alarms on the panel mate displays. Thanks for the confirmation.

 

[Mickey]

Another thing that can cause intermittent comm problems is leaving the "Autobrowse"
running in RSLinx. So after it makes a connection with your programming PC uncheck the autobrowse.