Replacing PLC5 w/ 1771-ASB - no Active light @ 230.4 kbaud

In preparation to migrate from PLC5 to ControlLogix, we are moving our PLC into a separate chassis, using a 1771-ASB in its place in the former rack 0&1 chassis. The ASB has been assigned to new contiguous rack numbers.

We added the new ASB to RIO channel 2B (230.4 kbaud) and the active light was off. We tried two other ASB modules and got the same results.

Out of desperation, we moved the rack over to RIO Channel 1B (57.1 kbaud) and the green active light came on.

Now the great mystery is... why doesn't this work at the higher baud rate???

This chassis contains several analog & specialty modules, including 1771-OFE2, 1771-IFE, 1771-NOC, 1771-NR & 1771-VHSC. I'm used to having these modules only in the local rack. Are one or more of these unable to work at 230kb? Any other thoughts?

Thanks in advance.

You did not say so I have to ask. Did you set the dip switches?

What series is your 1771-ASB. Series A and B do not support 230kb.

Channel 2B software configuration?

Mickey said:

You did not say so I have to ask. Did you set the dip switches?

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I understand - been there/done that. The dip switches were double checked by an engineer & an experienced tech. They even verified none of them were in limbo.

Mickey said:

What series is your 1771-ASB. Series A and B do not support 230kb.

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The first two we tried were series E. We didn't try 57kb with these. The one in there now is series B.

Mickey said:

Channel 2B software configuration?

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I am not sure the termination resistors would cause your issue but at 230kb the resistors should be 82 ohms.

Agreed. That network has been in use for years, so I'm told they are 82ohm resistors. I'll go check but (of course) three other crises have reared up today during this migration.

This isn't our first rodeo with replacing a 5 with an ASB. I'm simply baffled that this is the first time this issue has happened, to my recollection. I'd expect a wrong resistor would cause issues on all the other rack adaptors on that network but they're all fine. Not sure if a chassis could be limited to 57kbaud but I was a contractor here in '94 when this system was installed. There are 3 adjacent chassis in the same enclosure that were installed at the same time and they're all on that 230kbaud network.

One other thought... this new ASB is assigned to racks 13 & 14. (This chassis is and always was set up for 1-slot addressing, so that isn't new)

Years ago, racks 13 & 14 were on channel 1B (57kbaud) but were deleted from the channel configuration recently when that obsolete equipment was removed.

Is there something in the PLC memory that would prevent racks 13 & 14 from being used on channel 2B even AFTER they were deleted from channel 1B's configuration?

Usually the problem when you remove a PLC-5 and insert a 1771-ASB is the DIP switch pattern for the backplane switch. But since you examined it closely and the adapter works with a different scanner, that's not the problem.

Since logical Racks 13 and 14 don't have any adjacent logical Rack numbers, it's not an overlap problem.

It's interesting that you mention Racks 13 and 14 being in the Channel 1B scanlist in the past. You can't have part of a Rack number being scanned by more than one channel, like Rack 13 Groups 0-3 on Channel 1B and Rack 13 Groups 4-7 on Channel 2B.

So maaaaaybe there's a ghost of the configuration in Channel 1B that's causing a conflict. I'm not sure how to "purge" it other than maybe changing the Diagnostic data file, or forcing all zeroes into that data file.

One more thing; can you scroll/post/examine the whole Channel 2B scanlist ?

A RIO scanlist is limited to 16 logical rack numbers, and 32 total physical devices.

I read at least 13 Rack numbers in your scanlist. Rack 21 has two half-rack adapter devices, so it still counts as only 1 of the 16.

Adding Rack 13 and 14 would take you up to 15 devices.... so what's at the bottom of that scrolling Scanlist window is important.

Edit: the Windows Snipping tool is free and simple, but FastStone Capture has the nifty capability to scroll a window and capture the full extent of its contents.
http://www.faststone.org/FSCaptureDetail.htm

"Phinneas J. Whoopee, you're the greatest!" - Tennessee Tuxedo

Ken Roach said:

One more thing; can you scroll/post/examine the whole Channel 2B scanlist ?

A RIO scanlist is limited to 16 logical rack numbers, and 32 total physical devices.

I read at least 13 Rack numbers in your scanlist. Rack 21 has two half-rack adapter devices, so it still counts as only 1 of the 16.

Adding Rack 13 and 14 would take you up to 15 devices.... so what's at the bottom of that scrolling Scanlist window is important.

Edit: the Windows Snipping tool is free and simple, but FastStone Capture has the nifty capability to scroll a window and capture the full extent of its contents.
http://www.faststone.org/FSCaptureDetail.htm

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Ken, I think you found the issue! You (and others on this forum) have taken me off the hook numerous times and I am extremely thankful.

After Rack 21, we have rack 22, 23 & 24 all configured on this channel. I had to take off my shoes but by my count, that's 15 racks.

My co-worker tried an auto-config and it added rack 13 but not 14. Didn't make sense at the time but rack 13 would be the 16th rack, so I'm guessing that's why the software wouldn't add rack 14.

We're going to stick with the rack configurations as they are for now but this has me wondering: does that 16 rack/32 adaptor limit apply to the 1756-DHRIO module as well??? Due to time/budget constraints, we're upgrading the processor now and the RIO later.

does that 16 rack/32 adaptor limit apply to the 1756-DHRIO module as well ?

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Excellent question.

I believe that the 16 Logical Rack limit is mostly a PLC-5 restriction, while the 32 physical device limit is part of the RIO/DH+ signal transceiver design.

I found a note in the 1756-DHRIO User Manual that says it's limited to 16 devices per channel if certain older RIO devices (like 1771-ASB/A or /B) are on the link. But otherwise it can handle 32 adapters total, whether logical or physical.

That limit probably applies to the 1756-RIO and the AN-X RIO Scanner as well.