Communication problems between Schneider(Modicon) Twido and Weintek HM 1

[penkomitev]

Hello all!

I have troubles establishing communication between Weintek MT6070iH and Schneider(Modicon) Twido.
I admit the post is little longer at a glance, but if you take a closer look, it mainly includes settings. I just want to explain everything in a very descriptive manner so everyone understand what I have tried to do and probably understand why it’s not working ?.

Here is some specification of both devices in order to clarify how should things work:
Protocol: Modbus via RS-485(2W(wire)).
Baudrate: 19200
Parity: None
Data bits: 8(RTU mode)
Stop bits: 1

In the Weintek software:
• PLC Type: MODBUS RTU
• PLC device number: 5(This is used as address for the Modbus communication)
• RS-485 2W
• First COM1, then COM3 with the settings above for baudrate, parity, etc…

In TwidoSuite, in addition to the PLC and its expansions, I added a “General Modbus Element” which is actually the Weintek HMI. I created a link between it and Twido. Here are the settings I adjusted in TwidoSuite:
• Twido Port configuration – Modbus, Address @5(This is the address, therefore we set to 5 as we did in Weintek Software)
• Link configuration – using the same settings above for baudrate, parity, etc…, calling the network “PLC->HMI”
• General Modbus Device(the Weintek HMI) – Master

I followed the “Modicon Twido” wiring diagram in the PLC connection guide PDF which comes with the installation of the Weintek Software. I made two cables one after another, to test things out, but neither of them worked for the communication. Here are the wiring schematics of both cables:

Here is a link to the wiring diagram, but I include it as a text also: ftp://ftp.weintek.com/MT8000/eng/UserManual/plc_connection_guide.pdf Page 234.

Weintek COM1 RS485 port ? Twido 8 pin miniDIN port
Pin 1 RX- Pin 2 B(-)
Pin 2 RX+ Pin 1 A(+)
Pin 5 GND Pin 5 DPT, Pin 7 GND. Connecting these pins tells Twido that we are using the port for MODBUS and not for the protocol used for programming the PLC.

Weintek COM3 RS485 port ? Twido 8 pin miniDIN port
Pin 6 Data- Pin 2 B(-)
Pin 7 Data+ Pin 1 A(+)
Pin 5 GND Pin 5 DPT, Pin 7 GND. Connecting these pins tells Twido that we are using the port for MODBUS and not for the protocol used for programming the PLC.

According to my opinion, everything is to be watched from soldering side. This is the way I prepared the two sides of the cable.

After adjusting everything, I decided to upload both the PLC and the HMI applications to the devices and see if everything works. Unfortunately, no communication was established. The red “COM” lamp on the HMI was just blinking from time to time, but there was no persistent activation. I noticed that, if create a “Toggle” button, it is no visible if there is no communication from the PLC we have specified for this button.

After having no luck, I decided to try “ASCII” mode, because I noticed the wiring schematic is the same. When I started the HMI, the “COM” lamp was activated and there seemed to be some communication between the Twido PLC and the HMI. I was relieved because maybe I had finally solved it. I added several buttons to the HMI application and re-uploaded it, but by clicking them, there was no result. After a few minutes of tests, I noticed the “COM lamp is no longer activated and I couldn’t reproduce the situation in which I had this “strange” communication.

I would like to say, that this is the first use of MT6070iH Weintek HMI and maybe the forth use of Twido for our machines. On our previous machine, we installed the legacy HMI Weintek MT506TV. It used the same settings, the same diagram for soldering the cable and it works properly until now(it’s 2 months since we installed it). There is no logical explanation why these wiring diagram and settings would work perfectly on the legacy MT506TV, but would not on the new-generation MT6070iH.
As for the cable, it’s just 1 meter long, therefore I didn’t select a “shielded” one. However, I do not think this is the problem.

Okay, now to the questions. Does anyone ever used this combination of devices – Schneider(Modicon) Twido and a Weintek HMI? What wiring diagram and settings did you use? Was it a new-generation MT6000 HMI or an older model?

And some general questions – What is the best way to test MODBUS devices – PLCs, HMIs, other? How can I detect which device is the one not properly configured? Maybe some MODBUS testing devices, which I can use before cold starts? What would you recommend?

Thank you in advance!
Penko

 

[danw2]

1) >After adjusting everything, I decided to upload both the PLC and the HMI applications to the devices and see if everything works. Unfortunately, no communication was established.

Can I assume that you are able to successfully upload programming changes via RS-232 serial ports?

This refers to your inability to establish communications between PLC and HMI, not to getting programming uploaded?

2) >According to my opinion, everything is to be watched from soldering side. This is the way I prepared the two sides of the cable.

Aren't DIN connectors on the user side 'labled' with embossed numerals in the plastic identifying the terminal number on the user side (as opposed to solder side)? I would think that the external user side is illustrated in the manual, not the solder side

3) For an initial test, I would test the Twido slave for a legitimate response from a master by using a generic PC Modbus master program like Modscan 32 and a RS-232/485 converter.

 

[penkomitev]

@Danw2, thanks for answering.

1) Uploading programs to the HMI is done via microUSB port on the HMI device. No serial communication is included, so uploading and changing the application is okay.

2) Unfortunately, no numbers are visible on both sides of the miniDIN. In contrast, the 9P "COM" port is numbered and it's clear which pins I have to solder.

3) I downloaded something called "SimplyModbus". In fact, Twido is programmed via a USB to RS485 converter. Then, there is a software emulation of "COM"(it can be 1 to 20). I suppose I can use this original converter too. Maybe I have to turn the arrow to position 3 which is said to be for Modbus in contrast to position 2 which is for the Twido programming protocol. I will find the program you suggested too and try with it.

 

[danw2]

Simply Modbus is just as good. It does the same thing.

By 'soldered side', do you mean the solder side of a mating connector plugged into the HMI's connector?

 

[penkomitev]

@Danw2, yes under "solder side", I mean the side of soldering of the cable towards the 8 pin miniDIN male connector, which is connected to the 8 pin miniDIN female connector, located on the PLC.

 

[penkomitev]

I resolved it after two days of struggle .

It seems that the communication has been established all the time while I was using the COM1(but not when using the COM3 as there was a clear "no PLC response" window).

Anyway, the "COM" lamp does not stay active persistently, but just blinks with a rate, dependent on the "Timeout" you have specified in the settings. I have specified "3.0 seconds" and that's why I was blinking very slowly, seeming like there is no communication.

The second problem - the HMI makes invisible all objects, whose values cannot be read.

The third problem - Schneider Twido does not allow addressing elements which are not part of the program. For example, if you want to read the status of M50, it must take part in at least one rung in the ladder. Otherwise, you are not allowed to read its status.

Now, imagine these three problems combining each other. It's nasty! But I am relieved I was able to solve the problem. Moreover, I did it almost myself so the relief is even bigger.

Regards,
Penko

 

[danw2]

Good job. Thanks for the update.

Imagine trying to troubleshoot non-appearing objects, when the HMI makes them invisible . . . . That's a toughie.