Mitsubishi FX Communications Problems

ADCENG

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I have an issue getting an Automation Direct Touch Screen communicate over RS422 with a Mitsubishi FX-2N PLC. The touch Screen works with older PLC's of the same series, but not with new out of the box PLC's in the this series. I have heard that Mitsubishi changed their power supply and that it fluctuates. I can not confirm this. Does anyone know of any changes Mitsubishi has made?
 
I believe the power supply problems (read changes) are in the smaller FX1S series and is related to the 5VDC port power. This affected the MTA series manufactured by Bejier, and I suppose other similar units. I have not had problems communicating with the FX1S/ FX1N and the Automation Direct 6" monochrome touchscreen, as this is externally powered. Verify your port settings.
Good Luck
tommy23t
 
Thanks Tommy, same 3 customers, same settings three different FX series PLC's, same port settings, same cable. I have the same setup in my office as one of the PLC's, an FX-2N, and it woks perfectly with the customers' cables. One customer used our 25 pin cable with an 8-pin adpater, and it works. Trying to get details on that now.
 
The Newer FX PLCs have some strange communication defaults. The protocal is propritary and companies like Automation Direct have to reverse engineer it. This is done without the permission of Mitsubishi. I do know that if you download the PLC program with GX Developer Version 7 your Automation Direct HMI will work. Sounds strange but trust me, I've just been through this.
 
TomOstrowski or someone else

Can you give us more details what is different with new FX2N PLCs?

Is this a problem with Automation Direct only or we actually need a diffrent (newer) software and/or cables?

Is this a protocol only or something new in hardware/port configuration?
 
Tis seems to be isolated to newer Mitsubishi PLC's and EZTouch/EZText Panels. I have an older FX-2Nc and a brand new 2NC and the old one works, the new one does not. I get a PLC Message TimeOut. Another customer had this same issue, and he replaced the 9ft standard cable (no twisted pairs) with a cable he made with twisted pairs and it worked.

Now the simple answer is "well use a cable with twisted pairs!", but that is just a band-aid to a larger problem. Mitsubishi changed something, that in combination with a cable without twisted pairs seems to be the issue.

What did Mitsubishi change? They admit to nothing.
 
ADCENG
It looks really strange: twisted pairs can affect RS422 on larger distances, but I never saw problem with a few feet of cable.

SC09 cable does not have twisted pairs - does it work with new FX?
or we need something new to work with new PLCs?

May be they replaced RS422 comm chip with something different?
Or the issue is in 5V supply coming out of PLC?
 
The power supply is what I've been wondering about. Someone else suggested that Mitsubishi changed the comm chip.

We looked at it on a scope, and the one that communicates has sharp pulses with little ringing. The PLC that communicates intermittently is noisy, but both have a differential voltage of 9- 9.5 VDC which seems plenty high enough. Can the noise be coupling with the other signals since it's not twisted over 9 foot cable?

There is definitely a difference.
 
Have you tried looking at it with a communications analyzer? If not, that would be a good place to start. This would probably tell you right off if you are getting reflection and/or noise.
 
ADCENG
The "old" FX plcs had 330 Ohm resistor inside.
Second resistor was inside of the SC09 cable.
Any chance that they removed this resistor from the processor port?
Do you know what chip they using now?
It use to be 75179B.
9V is very high for RS422.

BTW can you enable your PM?
 
Last edited:
My eyes were crossed looking at the scope.

The FX-2N older 5.6Vdiff -2.8VDC to 2.8VDC

The FX-2NC newer 6.16Vdiff -3.08VDC to 3.08VDC

We just discovered that when te power ground on the 2NC is connected, our signal is very noisy and the peaks on the ringging is higher. This does not make sense, it is a good ground, same ground as the 2N.

Also discovered that the ground on the panel, which is 24VDC supply was disconnected. Connected the ground to the panel, and communication stopped dropping out.

Problem is, customer tried the same thing, and it did not help. Maybe a bad ground on his panel.

I'll have to look at the chips, thanks for the info.
 

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