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Old June 11th, 2019, 10:07 PM   #1
zacslade
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SLC 5/05 MSGing itself

Hi all,

I have a SLC 5/05 which stores encoder feedback for three off-brand drives in registers F27:0, 1, and 2. Those registers are populated via a MSG instruction, with the following setup:

-- This Controller --
Comm Command: 500CPU Read
Data Table Addr: F27:0
Size in Elements: 3
Channel: 1

-- Target Device --
Message Timeout: 23
Data Table Address: F6:0
Local / Remote: Local
MultiHop: Yes

(Control bits are all 0 except for EN, which is 1)

The multihop lines are:
From Device, From Port, To Address Type, To Address
This SLC 5/05, Channel 1, Ethernet/IP Device (str), 192.168.5.0
Logix Backplane, N/A, Backplane Slot (Dec), 0



So, I interpret all that to mean that this controller is using a message instruction to read data from itself, moving floats from F6 to F27. I go take a look at F6 to see what's there -- there is no F6. My registers from 5 to 7 are:

C5 (Counters)
R6 (Control)
N7 (Integers)

I had to look up what a Control Register does. I found the description in the manual linked below, and I can't imagine how this works if you have errors on more than one ASCII instruction simultaneously, but that still doesn't solve the mystery of how I'm getting these encoder values.

https://literature.rockwellautomatio...m001_-en-p.pdf

What's going on here? Where should I look next? Anybody seen this kind of setup before?
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Old June 11th, 2019, 11:43 PM   #2
sparkie
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That is a funky setup. I can't contribute much, but I was curious if there could have potentially been another controller receiving this information, and the devices were moved to this PLC. I would not do it, but I could see this being a fast and dirty way to change as little logic as possible.
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Old June 12th, 2019, 08:41 AM   #3
widelto
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What is your PLC IP address.
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Old June 12th, 2019, 08:53 AM   #4
Firejo
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You can get a SLC to message itself but not with the setup you are showing. When you add a MultiHop you are telling the MSG instruction to use CIP rather than PCCC (at least that's what happens when I try to duplicate what you've got setup). When I enable the MSG it errors saying the connection was broken which is what I would expect if it were trying to establish a CIP connection to itself. When I change MultiHop to "No" and enter the address of the SLC into the address spot it works and I can move data (although that is a very strange way to do it). Also, it fails, again with a broken connection message, if I enter an address ending in "0".
Is the IP address of your SLC "192.168.5.0"? It looks to me like it is communicating (or was communicating) with a logix PLC somewhere on the network although I don't understand the IP address ending in "0". That is pretty much never done and in fact some equipment won't allow it (I don't know about AB).
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Old June 12th, 2019, 08:55 AM   #5
Firejo
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The other thing (I forgot to mention) is that you can't address a register that isn't there. If you don't show an "F6:0" register it can't read or write to it.
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Old June 12th, 2019, 10:52 AM   #6
Ken Roach
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It doesn't make any sense to send a message from the controller to itself, and certainly not with a Source data table that doesn't exist.

This must have been a MSG intended to read from those drives (are they connected over Ethernet ?) and then abandoned during development, with an invalid multi-hop path.
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