FX Series RS422

[ADCENG]

We recently started receiving complaints from customers that the EZTouch Operator Panel will not communicate with the Mitsubishi FX series PLC's. Customers have no problem with older PLC's of the same series, but new "out of the box" PLC's will not communicate. I have heard that Mitsubishi changed their 5V power supply and that it fluctuates more and that this may be the issue, but I can not confirm this. The problem is centered around a 15 pin to 8 pin cable that was thought to be the issue. But I have tested 7 returned cables that work fine with my "older" FX-2N. The same customer used our 15-pin to 25-pin cable with a 25-pin ti 8-pin adapter and it works fine. Here is the difference, the 25-pin has twisted pairs, the 8-in does not. But we are only talking 9 feet. Has Mitsubishi changed something that in combination with a substandard cable is now causing a problem? Any suggestings will be greatly appreciated. Bobby Thornton AutomationDirect.com Product Engineer

[Crossbow]

There was a warning released on their website about using the 5VDC coming out of the CPU's serial port. Do NOT power an HMI off that power supply. It seems that some of their own E-termina operator interfaces were having the same problem ,and so they have a DC24V to 5VDC converter cable to power the HMI from a regular 24VDC power supply. Apparently on some units the 5VDC on the serial port can get as low as 4.7V. I will look for the announcement and forward it tomorrow from my work PC.

[ADCENG]

Operator Interface has it's own dedicated 24VDC Power Supply. This is an RS422 issue. The Operator Interface just will not communicate at all with a new FX series PLC. I have a setup in my office with an older FX-2N and it works great. But a customer with a new FX-2N could not get them to talk. I'm even using his cable which we thought was the problem.

[JimRowell]

Since your signature indicates your with AD, let me ask you this... Does the EZ-Touch use a full-blown, spec 422 interface chip or is it an in-house make-up? Perhaps you are both leaning towards opposite ends of the spectrum and now a change on Mitsi's end has the two of you too far apart (spec wise). An untwisted cable would exagerate that although I'm surprised that at less than ten feet it would be an issue. Try putting an isolator between the two (check out www.bb-electronics.com) and see if that fixes things up. That would suggest a voltage compatibility problem if it does. I've got an fx2n beside me with a 485BD board on it and the driver voltage is within spec but just barely with a light load on it. If your hmi interface is a really heavy receiver load, or puts out an even worse driver voltage than Mitsi does than problems could arise. Somehow I suspect that it's not related to any of the above since I can't say I heard anyone having problems along these lines before. Perhaps these customers havn't told you that they just finished installing a really, really noisy something-or-other right beside every display. If you had that piece of info, it might not be surprising that you now need a twisted-pair cable. If you are only talking about 2 customers, then as far-fetched as that seems, it's a possibility (I've had worse you-won't-believe-it scenarios happen to me). It would be interesting to see what effect an isolator has. Also, you should already have gotten yourself a brand-new plc to check this out further. See if it works on your desk. Maybe there are addtional environmental issues working against you. The cable should be ok. I've done 422 comms to the FX2N using wet string. No problems.

[ADCENG]

Jim, thanks for the suggestions. I am not very savvy when it comes to communications, but I have been suspecting that the EZTouch panel must be on the extreme end of meeting specs since it seems to be the only device that is having isses, and it seems to be related to newer Mitsubishi PLC's(even of the same model). An isolator is a great idea, I will try it. I have a new Mitsubishi on the way and am going to scope the old and new and see what might be going on. The environement is very clean from what I can ascertain from the customer. I did discover that he is using a Mitsubishi 25 pin to 8-pin converter in the line. It does not have external power, but it is definitely effecting the situation. Also, he make his own cable using twisted pairs and has no problem at all. If I can duplicate the problem, which is what has been the difficult part, I can test twisted and non-twisted. Thanks again for the reply. BobbyT.