DH-485 woes... add a ML1200 and it dies..

Hi guys,

Found the forum by Googling up answers, but I'm not seeing any good ones yet.

I have a DH485 network with 7 nodes on it. It has a variety of SLC's (01's/ 02's), one ML1000 and one ML1200. The SLC's are using the old AIC, while the ML's are using AIC+.

One SLC is a 5/04 being used as a 'data concentrator' gathering limited info from the others on the -485. The 5/04 then talks to RSView 32 implemented SCADA on the DH+ channel (through Linx Gateway).

I know... it's a typical mess that you run into with these old networks.

This config has worked well for over four years. Now, we're trying to add one more ML1200 to the mix. Nothing fancy... just a few messages back-and-forth from the ML to the SLC 5/04. They're not even implmented in the code as yet.

When I plug the ML into the AIC+... the network IMMEDIATLY starts getting Comm timeouts on various nodes. It doesn't do this whe the AIC+ (by itself) is connected.

All the diag lights on the AIC+ look good.

Someone at AB told me this might be ML1200 firmware issue (the fw is probably an old rev. from a re-used PLC). Might this be the case? They also suggested I change the station number (the added ML is the last one in the daisy and has a lower number than some of the others).

The net length appears OK... possibly 2500 ft. total. Cabling seems OK, terminations OK, grounding OK.

I'm stumped. Anyone seen this kind of thing before....?

John

Chect the new ML1200 communications protocol. If the new ML1200 is set up for AB_DF1, it will knock down your network running on DH-485. AB_DF1 is a point to point comms protocol that only wants to see 2 devices on the comms connection. You can hook the ML1200 to a panelview or other PLC through aa AIC+ module and it will work fine, when you plug in your laptop to make a 3rd node on the network something will drop out.

I will check that out... but I doubt that's the problem.

When the net went down today I had to reset the comms back to the factory default (DF1) so I could talk to the darn thing.

I wondered about the cable from the ML1200 to the AIC+, too. They're using the -AP-00 cable (this has the little mini din on the ML1200 side and the 9 pin -232 on the AIC+ side. All we've ever used before is the din-to-din.

Thanks,

John

You have to be careful with the cable from the PLC to the AIC+. Apparently the standard A-B cable also includes power connections, and this can bring the network down. On a recent project we had to replace the A-B cable with a custom built one that only had the three data conductors (RX, TX, and GND) and then it all worked fine.

Update...

After speaking with AB today.... they are getting harder to get on the phone these days... We got a fix going.

The ML1200 had a series A rev. 2 OS onboard. That was a very early release.

Downloaded a new OS from the website.

When it was flashed to series C rev. 11 the problem disappeared.

Daggone it... now I'm going to have to check other ML's other there to see if more problems are lurking on older units (-;.

Thanks for the info.

John Kelley