Modbus TCP & Starting Address

[gautlabview]

Hi all,

I need your help to read a temperature on a climatic chamber.

For this purpose, I use Labview 2020 and the Modbus / TCP Protocol, with the DSC module.

And I have this error : APPEND Function 3

Code : -389120

The computer recognizes the chamber but I don't receive any data. So I suppose that I don't have the right starting address. Or maybe the error is in the block diagram.

The chamber designer has given me a CANID table. And if I need to read a temperature, I have the number 0x11400080.

After a few researches about the CANID table, I have found that 0x80 was supposed to be the starting address. I also tried 7F, 00, 01, 11400080, ... but I do not find the right starting address. I always have the same error in the "Read Holding Registers" block.

Can someone help me to find the right starting address or the block diagram error ?

Thank you very much !

[RTSLVU]

CANID table? Are you using Modbus or CAN bus?

Usually with Modbus you would have a "register map" as part of the documentation. That would tell you what holding registers hold what measurements.   

[gautlabview]

Hello RTSLVU,

I'm using Modbus, I think you're right and the CANID table is not useful.

I had the error -389120 on the port I used, 502, and I changed it by 10001 as specified in the manufacturer's documentation and now I have the "famous" error 56 (timeout), regardless of the address (it is written that the modbus address should always be set to 1 in the modbus tcp part so I think it should be 0x01... but no matter what address I put, I get the same error).

So I tried to ping my chamber, and everything is going well.

And then I used Wireshark to look at my frames. And I have TCP Out-of-order for the request and TCP Zerowindow for the response. Maybe it can explain my problem.

I keep looking for solutions but If you have any idea, it would be great !

Thank you

[GerdW]

Hi gaut,

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@gautlabview wrote:

I had the error -389120 on the port I used, 502, and I changed it by 10001 as specified in the manufacturer's documentation…

I keep looking for solutions but If you have any idea, it would be great !

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Why don't you attach the manual, when you want us to help you with your problem?

[Sebastian.Weber]

Hi!

Did you try any other modbus client? I'm using "CAS Modbus scanner" to cross check MODBUS communication. 

[gautlabview]

Hi GerdW, Hi Sebastian Weber,

Here is the manufacturer documentation.

I didn't try CAS modbus scanner, I'm going to download it and see what we get.

Thank you

[gautlabview]

Here is the result of the Modbus scanner.

So there is a timeout issue 😕 I don't know how to fix it...

[Sebastian.Weber]

Hi!

The manual is a bit strange... It always talks about Modbus RTU and Serial MODBus data tunnel

There are three types of Modbus protocols: MODBUS RTU, ASCII and TCP.

RTU and ASCII are used over serial connections like RS485, and TCP over network. (Really!)

The data packets are different for all three types.

Is it possible that your device does not support MODBUS TCP, and instead expects MODBUS RTU packets being sent over network?

I'd ask the manufacturer for an example about what bytes are expected here.

[gautlabview]

Yes that's a problem, but there is an Ethernet port on the chamber and the manufacturer uses two types of Modbus on their own software (RTU and TCP). But their software is not enough for what I want to do. But I'm pretty sure that Modbus TCP is possible...

And If I want to use Modbus RTU, I have to pay to take the RS-485 option... that's why I'm trying to use Modbus TCP...

By the way, I just tried Wireshark with the port 502 and even If I have a lot of errors, I can see my query and my response?! Does this mean that Modbus TCP is possible?

Thank you 🙂

[gautlabview]

Tomorrow I will install the manufacturer's software and compare their frames with mine. Maybe it can solve the starting address question.

If you have any other ideas, I'm interested.

Thank you !