1756-RIO & DH/RIO placement?

Duranthas · Aug 27, 2021

I'm just wanting to bounce this off the collective wisdom, but am I correct in thinking that a 1756-RIO and a 1756-DH/RIO do not have to be last in the daisy chain? I'm like 99% sure that it shouldn't matter where they are physically located in the chain but I wanted to confirm before I make my Belden 9463 purchase. I was thinking that the most important parts were that they terminate with a resistor, and that the length doesn't exceed the prescribed distance for that baud.

OkiePC · Aug 27, 2021

I believe you are correct. I don't have a lot of first hand experience with either, but have heard it reported that the 1756 cards that support blue hose are more sensitive to having proper termination than the old 1771 hardware was.

I have seen many PLC-5 RIO and DH+ cables with missing termination, star networks and other ill-advised installations that worked just fine. I've been told that we shouldn't try to bend the rules with the newer stuff.

Bit_Bucket_07 · Aug 27, 2021

Duranthas said:
I'm just wanting to bounce this off the collective wisdom, but am I correct in thinking that a 1756-RIO and a 1756-DH/RIO do not have to be last in the daisy chain? I'm like 99% sure that it shouldn't matter where they are physically located in the chain but I wanted to confirm before I make my Belden 9463 purchase. I was thinking that the most important parts were that they terminate with a resistor, and that the length doesn't exceed the prescribed distance for that baud.

That is correct.

Operaghost · Aug 27, 2021

Yes, the DHRIO and RIO can be anywhere in the daisy chain. And to be clear, the network should be terminated at each end. Devices in the middle must not be terminated.

I have been on troubleshooting calls to a customer site where someone has added additional devices to the previous end of the cable but failed to move the resistors. They had the infamous, "but it's been working" response. It worked, until it didn't.

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1756-RIO & DH/RIO placement?

Duranthas

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OkiePC

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Bit_Bucket_07

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Operaghost

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