PLC-5 Ethernet IO

phuz

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Jun 2008
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Could someone please confirm that PLC-5 Ethernet IO is not possible? I spoke to someone yesterday who insisted it was and that they had actually done a project with it. From what I see, the 1785-ENET is only usable as an interface module for connecting to PLC2/3/5 controllers, but cannot be used for IO only.
 
I think it was Tom Jenkins who said you could lift the Empire State Building with a 1/2HP motor in theory with the right gear reduction.

I won't say it is impossible that someone has controlled some ethernet I/O using a PLC-5, but I am pretty sure it wasn't "by the book" EthernetIP as is done with a Controllogix or CompactLogix controller.
 
It wouldn't surprise me if there is a way to do it, but I wouldn't trust it. As OkiePC said, it wouldn't be EthernetIP. I had some drives that were Ethernet (not IP) controlled from a PLC5. Since it wasn't IP, the PLC5 and the drives didn't really know when they had lost comms with each other - at least not in any acceptable timeframe.

Without EthernetIP, its like your wife talking to you while you're watching the game...you don't realize that she is talking to you and she doesn't realize that you aren't listening.
 
There are third-party products, such as the Prosoft ANX2, for connecting PLC-5 via Remote I/O to Ethernet/IP devices like drives and Panelviews. This would not use the ENET sidecar, and I don't think it is really what you are after. It's worth noting if you have a situation where a supported device needs to be replaced, and the RIO interface is no longer available.
 
Could someone please confirm that PLC-5 Ethernet IO is not possible? I spoke to someone yesterday who insisted it was and that they had actually done a project with it. From what I see, the 1785-ENET is only usable as an interface module for connecting to PLC2/3/5 controllers, but cannot be used for IO only.

If someone ever accomplished Ethernet remote IO control on a PLC5 platform (and I am pretty doubtful when stating this!) it was probably implemented using PLC5Es. The 1785-ENET 'side cars' are merely PLC5 Ethernet connectors for application level communications.

'Regular' PLC5s processors communicate using PCCC (Programmable Controller Communication Commands) application-level commands; PCCC communications are not connected but requiring of a explicit, programmed data transfer mechanism as opposed to the 'implicit' type, cyclic (scheduled), UDP/IP driven EtherNet/IP type communications used by the Logix Class controllers.

Ethernet TCP/IP connectivity was originally added to the SLC5/05 and PLC5E using the proprietary Client Server Protocol (“CSP”) protocol, with embedded PCCC commands.

The PLC5Es and SLC5/05s support both CSP and EIP protocols (“dual-stack”) concurrently on the same Ethernet cable at the same time, however, personally, I am pretty sure that even if PLC5E, SLC 5/05 and MicroLogix (via NET-ENI) CPUs support EtherNet/IP messaging, they do not support IO data transfer the way Logix CPUs do.

We are aware that there are Explicit Messaging 'IO control' (mainly VFDs) implementations out there which apparently serve the intended purpose, however, these are merely 'unsound engineering' exceptions.
 
I am 100% certain that the PLC-5 cannot control I/O on EtherNet/IP in the same way that ControlLogix and CompactLogix controllers can.

I agree that there are a handful of both sound and unsound engineering techniques that could stretch the definition: sending MSG instructions to AC drives with the PCCC object, or adding a Prosoft Modbus/TCP module with third party I/O, or using a RIO gateway of some kind.

But the built-in Ethernet port on a PLC-5E, or the 1785-ENET sidecar, or the serial 1761-NET-ENI... none of those have an I/O scanning function.
 
dmargineau: Side cars can do CIP E/IP messaging if the card, and the processor are the right revision. Rockwell AnswerID 7983, 61405,66899 have more details.
Processor has to be minimum Series E, Rev D.1, Series D rev E.1, Series C, rev N.1 (This is valid for PLCEs as well).
Sidecar has to be Series A rev D or higher, or any Series B or higher (Series C being the one with RJ-45 and 100Mbps support).

I have messaged between PLC-5 with sidecar and ControlLogix (which has to be CIP because AFAIK ControlLogix can't do PCCC ethernet messaging), but I've never done Ethernet IO direct from PLC5. My understanding it's technically possible, but extremely un-recommended, and there's a lot of manual work to it.

I have an engineering company claiming they've done it before with VFDs, and want to start our PLC5-CLGX migration that way: replace 20-COMM-R cards with 20-COMM-E cards, controlled by the PLC-5 over the existing sidecar. I'm curious to see how they did it, purely to see that it can be done, not because I want it.

I've had luck with migrations in the past where we start moving RIO racks and drives to Ethernet IO controlled by a CLGX, and the IO table is messaged to and from the CLGX which essentially acts as a mailbox. Once all the IO is migrated, the process control logic is moved to the CLGX. Care has to be taken to handle message timeouts, as the standard timeout is unacceptable for IO.
 

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