Micrologix 1500 1761-NET-AIC+ Issues

[dansomerville]

A customer of mine has a ML 1500 LRP connected to a Net-AIC+ via the mini din connector (CH 0 of plc to port 2 of AIC) from this AIC then connects a a bunch of other networks via Port 1. This is all working fine. The PLC port is configured as DF-1

My issue is that I need to connect to the PLC and view the code online. I cannot do this because the machine cannot run without the devices connected via the AIC to Ch 0 of the PLC. I have come to the conclusion that I need the LSP to do this easily. However, they had another AIC+ here already. Thought it would be a simple hookup but I cannot get it to work.

I have connected them together via port 3 with the proper wiring. Not showing any errors and the status lights flashing as they should. I cannot connect to the PLC through this though. Have tried the following combinations.

1761-CBL-PM02
Null Modem Cable
with RS-232 to usb converter. Both cables are good because I can connect to the PLC with the PM02 cable directly on the PLC and the Null Cable if I pull the existing cable off of the first AIC+ and plug it into Port 1

I have also tried connecting with my 1747-UIC and it does not work.

Is this combination even possible. Im guessing the issues are related to the PLC port being configed as DF-1 and this not being able to be passed to the second AIC+

Any help would be appreciated. I will get the LRP but dont want to wait a few days when I feel like I could have this solved now

 

[Ken Roach]

What are the other networked devices ?

Are you certain they are 1761-NET-AIC isolators, and not 1761-NET-DNI DeviceNet interfaces ?

Most networks built with those 1761-NET-AIC isolators use DH485 protocol, so you can plug in to one of the isolators with your 1747-UIC and go online with any of the networked devices.

You wouldn't see "flashing" LEDs but rather steady green, as the network token passing pretty much creates constant network traffic.

But a DF1 network might be DF1 Half Duplex where one device is a Master and the rest are Slaves, or it might be set up as a kludgy DF1 Full Duplex network where it works only by careful programming or by coincidence.

Your statement that you can connect to the PLC directly with a 1761-CBL-PM02 cable supports the idea that it's a DF1 Full Duplex network. You could create such a network using Net-DNI DeviceNet interfaces, which is one reason I asked.

If this really is a DF1 Full Duplex network with Net-AIC modules, then there's almost certainly no way around the issue without getting a two-port 1764-LRP controller. The Full Duplex protocol is meant for point-to-point connections and your computer will promptly interfere with any of the MSG instructions being triggered by devices on the network.

 

[dansomerville]

Thanks for the response, you confirmed my suspicions.

Both are AIC adapters. And yes, the network is setup as DF1 full duplex. It is connected to a series of legacy devices including a panel pc running windows 2000.....I'm not getting into that stuff, I just need to setup a few signals from a machine we are integrating downstream. Just wanted the ability to watch it online without having to swap cables all the time

I have already ordered an LRP processor with the second port.

 

[Ken Roach]

This network probably functions by coincidence.

As I mentioned, DF1 Full Duplex is, well, full-duplex. It is meant for a point-to-point connection where each device can transmit and receive at the same time. Most DF1 Full Duplex communication drivers actually ignore the destination and source bytes.

Net-AIC isolators with their 3-wire RS485 link are by definition half-duplex devices. They can transmit, or receive, but only one at a time.

You can put two DF1 Full Duplex devices onto a physical system that has a half-duplex wiring link, and they'll function most of the time if one of them is initiating all the messages (like an HMI or a programming computer).

But multiple devices ? There's no hardware or protocol method for keeping their transmissions from colliding with one another. It's like having to people talking to you at the same time.

So a system with multiple Full Duplex devices on a half-duplex link *can* work, but generally it's because the devices have been configured with large numbers of retries and long timeouts, and the devices simply suffer the collisions and errors. It's like old-fashioned hub-connected Ethernet, except at 19200 bits per second.