ControlLogix with PLC-5 Remote IO over ASB module

[mylespetro]

Hey everyone, ran into something I've never seen before and was wondering if anyone had any idea of what's happening.

Currently in the middle of a phased upgrade from a PLC-5 to ControlLogix where we have a ControlLogix chassis with a DHRIO card and we replaced the PLC-5 processor with a 1771-ASB (Series B) RIO adapter and are continuing to use the PLC-5 I/O cards as Remote I/O to the CLX.

The existing PLC-5 rack was configured as 2-slot addressing with Complementary I/O, no RIO racks in the original install. So we have a Rack 0, with module groups 0 through 7, and module groups 0 through 5 each have a 1771-IAD (16 bit digital AC input) and 1771-OAD (16 bit digital AC output), group 4 being an exception in that it only has an input card in the left slot of the module group, no output card in the right slot of module group 4. I've attached a picture of the chassis for reference.

I bench tested this with an identical CLX chassis and an equivalent 16-slot PLC-5 chassis, replacing the PLC-5 processor with a 1771-ASB module, and was able to connect the PLC-5 chassis as Remote IO in the CLX program. I didn't have any of the 1771-IAD/OAD cards though, so I could not bench test the I/O configuration exactly as it is in the field.

When I went to swap the customer's PLC-5 in the field, I got the ASB module to connect, but the module would connect as expected for about 3-5 seconds (green "Active" light would be on and solid), and then simultaneously the ASB's "Active" light would flash and the "ACTIVE" indicators on only the 1771-OAD output cards would go out. Regardless of what state the ASB module "Active" light was in, I could see both the current inputs and outputs present on the cards, although I expect the outputs were being held due to the chassis DIP switch configuration (hold outputs in last state during comms fault). For example, Rack 0 Group 0 Input 15 was present on the PLC-5 I/O, which was mapped to R_0:I.Data[0].13/I_000_Bit15 in my ControlLogix program, which was being read as a 1. When I went to the Channel A Protocol Errors tab in the 1756-DHRIO card configuration, the only thing that was coming up was that the "Non-Octet Alignment Error" counter was counting up. On coming back to the office to try bench testing again, I have no issues and no errors counting up in the tab.

For further reference, my ASB module DIP switch settings were as follows (both for in the field and bench testing):

SW1
1 - ON (1&2 always on)
2 - ON (1&2 always on)
3 - ON (Primary chassis)
4 - ON (I/O rack number 0; 4/5/6 on for this rack number)
5 - ON (I/O rack number 0; 4/5/6 on for this rack number)
6 - ON (I/O rack number 0; 4/5/6 on for this rack number)
7 - ON (First I/O group number 0; 7/8 on for this group number)
8 - ON (First I/O group number 0; 7/8 on for this group number)

SW2
1 - ON (57.6k baud)
2 - OFF (Complementary chassis - just seeing this now, should this match DIP switch 3 of SW1?)
3 - OFF (3&4 always off)
4 - OFF (3&4 always off)

And my PLC-5 chassis DIP switches were as follows (both for in the field and bench testing):

1 - ON (Outputs in last state during comms fault)
2 - ON (Processor can restart I/O chassis after comms fault)
3 - OFF (3&4 always off)
4 - OFF (3&4 always off)
5 - OFF (2-slot addressing; 5/6 off for 2-slot)
6 - OFF (2-slot addressing; 5/6 off for 2-slot)
7 - OFF (7&8 always off)
8 - OFF (7&8 always off)

Sorry for the wall of text, just trying to give as much information as possible.

Thanks in advance!

EDIT: No idea why my picture attached upside down

 

[Ken Roach]

My guess is that the Complementary Chassis selection is handled differently by the 1771-ASB than the PLC-5/12.

"Complementary Chassis" was an old memory conservation method that allowed you to install two physical chassis that shared the same "Rack" address, but split the Input and Output image tables.

So you could have one chassis that was all Inputs, and another chassis that was all Outputs, but they'd both be addressed as the same "Rack" number.

Or you could install modules alternating I/O/I/O in one, and O/I/O/I in the other.

You said your system never had any remote I/O modules, so it was just the processor-resident chassis set up for both 2-Slot Addressing (alternating Input and Output is conventional for that mode) and as a Complementary chassis.... but it had no complement on the RIO network.

I've never run into this exact configuration or migration, but my instinct is to set the DIP switches to turn off Complementary mode, and just treat this like a very ordinary 2-Slot addressing mode chassis.

 

[mylespetro]

Thanks Ken, I’ll give that a try when I’m onsite in the morning and update with the results.

 

[Ken Roach]

My recollections are coming back to me: I don't think that the 1756-DHRIO actually supports Complementary RIO adapters.

Which is OK, since your old PLC-5/12 system didn't actually have Complementary I/O anyhow, just ordinary 2-Slot Addressing.

Instead, the 1756-DHRIO ignores the Complementary mode switch on the 1771-ASB SW2-3, and treats the DIP switch SW1-3 as part of the RIO rack address; when it's set = ON, the rack address adds 10 (octal).

So your rack is 10, not 00. Does that conflict with another adapter device on the RIO network ?

You need to set up the 1771-ASB as indicated in the "without Complementary I/O" DIP switch setting diagrams in the 1771-ASB user manual.

And of course you're using an older 1771-ASB Series B, so the DIP switch settings and functionality are different from Series C and later. Be certain you're looking at the correct diagram in the User Manual, since they look so similar.

 

[Ken Roach]

Also: a "non octet alignment error" means that the 1756-DHRIO is seeing series of pulses on the RIO network that don't line up into 8-bit frames. That is, "these packets aren't an octet".

It indicates damaged hardware, interference, or bad cabling. It's not something you can ignore and expect reliable performance.

 

[mylespetro]

Thanks again Ken, I was kind of scratching my head over why the Rack Number tables in the ASB module manual started at 1 for Complementary I/O, whereas the tables started at 00 for systems without Complementary I/O.

 

[mylespetro]

So your rack is 10, not 00. Does that conflict with another adapter device on the RIO network ?

Also, this doesn’t conflict with anything, this is the only RIO connected to the CLX. I will change it to be non-complementary as you mentioned, set to rack 00. Thanks again Ken, as usual, your input is always extremely helpful.

 

[mylespetro]

Sorry for the triple post, but I'm looking at the 1771-ASB manual again and looking at Figure B.8 (ASB Series A/B for PLC-5 without complementary I/O), and it also starts at I/O rack number 1, where I was expecting to be able to address it as rack 0. I do see that the Series C/D without complementary I/O allows for rack number 0 (or specifically 00), is this a limitation of the Series B? I'm almost positive that my bench test ASB module is a Series B, which was the reason I ordered them for the project, since I knew it worked on the bench test. I'm unsure whether or not I could just leave the first 6 DIP switches ON to get a rack number of 0 or not, because for a rack number of 1, they are all on except for switch 6, which is off.

 

[Operaghost]

From my recollection, Rack 0 was always reserved as the local chassis for the PLC-5 CPU. Though you could force it start at 1 but you lost 0 in the process. You were not able to pick up unused portions of Rack #0 in a remote chassis. For example, an 8-slot chassis setup for 2-slot addressing with a PLC-5 in the left-most slot would only use Rack 0 groups 0-3. You were not allowed to setup a remote chassis to pick up with Rack 0 group 4. You had to start the remote chassis at Rack 1 or greater.

The different generations of controllers have resulted in differences in what can start with rack #0 and what must start with rack #1.

The PLC-5/10 had no remote I/O capability whatsoever.

The PLC-5/12 could not have any Remote I/O. It could only act as an adapter to another PLC. This was called Adapter Mode.

I seem to remember the PLC-5/11 could only have remote I/O Rack #3 (yep, just confirmed that). Racks 0-2 could only be local. Rack #3 could be local or remote.

The other PLC-5 controllers could scan remote chassis starting at Rack #1, but the 5/250 along with the PLC-3, SLC 500, and Logix 5000 all allow remote chassis to start at rack #0.

I think the PLC-2 also started with Rack #1.

OG

 

[mylespetro]

I figured it out, and it definitely wasn't a missing 150 ohm resistor

Thanks Ken and OG, should have been the first thing I tried, I didn't realize it didn't get put on, even though I was standing there face-to-face with the ASB module connecting and disconnecting the wiring arm from it every time I changed the DIP switches.