AB Data Highway Question

Join Date
Oct 2019
Location
NC
Posts
6
I seek the wisdom of the old men on the mountain.


I am working with an old data highway network while upgrading from PLC 5 to 5000. In order to message over some status bits during a drawnout upgrade, I slapped a DH/RIO card in my 5000 rack. I assigned this new DH/RIO card an address of a known decommissioned machine (as to not have a duplicate address), and spliced it into the network (Channel A). Shortly after doing this, one of the machines on the other side of the plant started to lose communication on its own remote network (RIO).



I am having to teach myself about all of this. My question to the wise men, is when addressing a Data Highway network, do the nodes have to be addressed in the same order as the physical machines are wired to the network, or can they be given any number, so long as there are no duplicate addresses?


Thanks!
 
Neither particularly old nor on a mountain :) I'd like to think I have occasional acquaintance with wisdom, though there's plenty around here with more.

Glanced through the manual for the 1756-DHRIO and I don't see anything regarding requirements for the address beyond the obvious "0-77 octal" and "no duplicates".

Node address shouldn't affect RIO regardless from what I know.
 
Old men on the mountain
...just experienced!

Cut and Spliced, eh?

Poor Data Highway network, being butchered like that...

I take it the cable is not an end-of-line? No resistor required?

Are the wires in the correct order with no stray wires touching the wrong core?

If all is OK, then unplug the DHRIO and see if the network recovers without it.

Duplicate addresses are not good, but nothing will tell you, not like ethernet networks. I used to have a diagnostic card and software for DH+, but that was back in the dark ages, when computers were not very personal...
The addresses do not have to be in a particular order.

Sketch what you have done, including addresses - pictures do help our old eyes....
 
No requirement, or any order for using node addresses. Any available address can be used. If I remember correctly, there was a slight performance hit when skipping numbers. But it was minimal and not anything we ever concerned ourselves with.

My initial thoughts are that since everything worked before, the splice is the most likely cause. Check all the connections and then verify resistors are properly installed at each end (none in the middle).

The DHRIO will tell you if it is unable to get onto the network because it is using a duplicate address. But it cannot tell you if another device is duplicating it's address.

What I mean is, if another device is powered on and using the same node # the DHRIO will scroll a message on the display. However if that other device is powered off and the DHRIO powers up, it will take that address and when the other device powers on, it will be the duplicate. The DH+ indicator on any device will turn red when it has a duplicate address error. But the DHRIO will not know the other device is in error.

OG
 
here's trick that the PLC-5 platform will do - to show you which Data Highway Plus stations are active ...

and I have seen PLC-5 systems use blue hose with ZERO problems for years with NO resistors installed ... BUT ... seems like DHRIO modules are VERY picky about having the resistors properly installed ... and you have to use the proper size resistor for the different baud rates of DH+ ...

also - (no offense intended) are you sure that you've got the rotary mode selector switches on the DHRIO module set correctly? ...

and I concur that Data Highway connections SHOULD not affect Remote I/O communications ... make sure that you're not mixing apples with oranges with your cable connections ...

good luck with it ... I've got to get back to my mountain (if I can just remember how to get there) ...
.

active nodes.PNG
 
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Lots of good information above. As dry as they can be, I recommend reading through some manuals, though they have some conflicting information.

PLC-5 Enhanced manual: 1785-um012 Chapter 9.
1756-DHRIO manual: 1756-um514
DH / DH+ /DH II/ DH-485 Cable installation manual 1770-um022

To answer your immediate question, no the node numbers don't have to line up with where they physically are in the network. Just no duplicate node numbers.

Basics:
-Use Belden 9463 Blue hose cable
-The signal is sent between the blue and clear wires. The shield is there to shield against noise.

-With DH+, convention calls for clear on terminal 1, and Blue on terminal 2. RIO is blue on terminal 1, clear on terminal 2. Electrically it doesn't matter as long as all nodes are the same.

Network wiring should be one of two formats:

Dropline-trunkline: No more than 3 cables leaving station connector. Two trunklines to the next SC boxes, one dropline to the PLC node. At each end of the network there should be one trunkline coming in, one termination resistor, and one dropline.

Daisy chain: RIO is commonly wired like this, though it is a legal configuration for DH+. Connections should have either have two blue hose connections, or one blue hose and a termination resistor.

Runs should be a minimum of 10 ft, with droplines no more than 100ft. The standard says not to mix dropline-trunkline, and daisy-chain, but it's usually not a cardinal sin. DH+ can take a lot of wiring abuse before it fails, so in the case of failure everything should look textbook.

Termination resistors
All networks must have termination resistors at the two physical ends of the network (in the Station connector boxes in the case of trunkline dropline, or on the nodes themselves with daisy-chain) . Some devices (Classic PLC-5) have internal termination resistors that can be activated by dip switch setting so the absence of a physical resistor doesn't mean it's not there.

Links at 57.6k or 115k with "older devices" should be terminated with 150Ohm resistors.

Links at 230k, or where the whole network is newer devices (basically anything capable of 230k like DHRIO and PLC-5 Enhanced) should be terminated with 82Ohm resistors. I've seen a note that 1756-DHRIO can work better with 82Ohm if the network can support it.

Troubleshooting
-Check for stray wires potentially shorting between terminals and resistors, and loose connections. I've seen DH+ and RIO mostly work when one connection was completely broken on the blue or clear, and others where it mostly worked when terminals were not near tight.

With a meter on Ohms you should measure the following:
-Very high impedance between shield, and either blue or clear
-What may appear to be a short between blue and clear.
-High impedance between ground and any of the connections.



Station connectors capacitively couple shield to ground. Shield could probably be solidly grounded at one point only, but this isn't called for in the standard. Clear and Blue should not be grounded, nor should have any voltage on them (a stray connection to a 24V or 120V supply).

If you measure a short between shield, and blue or clear, you may have a crossed wire at a node. I've seen a DH+ that worked for over a decade at 57k with a node that had clear and shield (using clear heatshrink!) swapped, but caused problems when the speed was increased to 115k. The DHRIO card on that network would become slower, and slower, and slower, and stopped responding. Both the LED display, and through RSLinx! Is your node with a malfunctioning RIO a 1756-DHRIO card on your DH+ or a PLC-5? PLC-5 seems very immune to problems on other channels, though the above problem could make the entire DHRIO malfunction.

A DH+ node powered off and disconnected from the network will measure 8 ohms (or is it 4?) across clear and blue (1 and 2). Your whole network with all devices' 3 pin phoenix connector unplugged should measure the parallel equivalent of the two termination resistors between blue and clear, and nothing between shield and either blue or clear.


Ron explains how to look at Active nodes in Channel 1A of a PLC-5. If you have a PLC-5 enhanced set a channel status file. The same active nodes are hidden in the data table but useful if you're on a channel other than 1A, and it will also show retries, etc that can show the relative health of the network.


Advanced Troubleshooting
A 1784-U2DHP can be used with the software "NetDecoder" to analyze packets on the network, but it sounds more like a connection issue. However Netdecoder can highlight issues like hammering messages that could overwhelm buffers on certain devices.
 
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Lots of good information above. As dry as they can be, I recommend reading through some manuals, though they have some conflicting information.

PLC-5 Enhanced manual: 1785-um012 Chapter 9.
1756-DHRIO manual: 1756-um514
DH / DH+ /DH II/ DH-485 Cable installation manual 1770-um022

To answer your immediate question, no the node numbers don't have to line up with where they physically are in the network. Just no duplicate node numbers.



Advanced Troubleshooting
A 1784-U2DHP can be used with the software "NetDecoder" to analyze packets on the network, but it sounds more like a connection issue. However Netdecoder can highlight issues like hammering messages that could overwhelm buffers on certain devices.
The Mountain Troll has managed to exit his cave dragging his Frontline bag of goodies. I agree with all of the good information above and add that if the original status is unknown you could start at the beginning and tick of items. Frontline and other tools are very useful in this scenario. I had to resolve issues with DH+ and a separate machine with CCLink both machines had multiple stations and both had been modified without due care. Netdecoder with appropriate probe has proved to be a lifesaver frontline tech support are awesome. Good luck with your issue.
 
Lots of good information above. As dry as they can be, I recommend reading through some manuals, though they have some conflicting information.

PLC-5 Enhanced manual: 1785-um012 Chapter 9.
1756-DHRIO manual: 1756-um514
DH / DH+ /DH II/ DH-485 Cable installation manual 1770-um022

To answer your immediate question, no the node numbers don't have to line up with where they physically are in the network. Just no duplicate node numbers.



Advanced Troubleshooting
A 1784-U2DHP can be used with the software "NetDecoder" to analyze packets on the network, but it sounds more like a connection issue. However Netdecoder can highlight issues like hammering messages that could overwhelm buffers on certain devices.
The Mountain Troll has managed to exit his cave dragging his Frontline bag of goodies. I agree with all of the good information above and add that if the original status is unknown you could start at the beginning and tick of items. Frontline and other tools are very useful in this scenario. I had to resolve issues with DH+ and a separate machine with CCLink both machines had multiple stations and both had been modified without due care. Netdecoder with appropriate probe has proved to be a lifesaver frontline tech support are awesome. Good luck with your issue.
 
I am going to say that the problems on the RIO network on the other machine is most probably not related to anything you do on the DH+ network.

The only direct relation between DH+ and RIO would be if pass-through has been configured somewhere. But I cannot see how that should affect the basic RIO data transfer between scanner and adapter.

Only thing could be if you while changing the DH+ network you unintentionally have been pulling on RIO cable(s), thereby having a connector come loose somewhere.
Other than that, it is a coincidence.
 

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