topic Re: Modbus Labview Program in LabVIEW

Modbus Labview Program

happinesss — Mon, 30 Apr 2018 10:55:44 GMT

Hi everyone, I have some Modbus Labview program that controls the heat flow and temperature and I couldn't understand the working principle of that VI. I searched a lot. I look at modbus holding register address format, Modbus wiki,MOdbus and etc but I couldn't solve the system. I put the snippet below. Can anybody explain what is the 5,9,11,17 and in the case structure 1,2,3 and 4 stand for? And in create serial master vi, there is parity and flow control part. The 'time left' and 'program' should be indicator but in here it is control. The RS 485 adapter is used. I couldn't understand all of them with respect to the internet pages that I searched. Can anybody give me a detailed explanation? What do we expect? Thanks in advance.Modbus

Re: Modbus Labview Program

jay0909 — Mon, 30 Apr 2018 12:03:10 GMT

Hi,

Lets break down step by step.

1) Intialise the Connection using COM3.

Inside the while loop:

2) Read Holding Registers.vi : This subvi is used to read the register information, Well there are 4 Inputs [(connection ref and error ), (Starting Address and Number of registers to read)]. In your program the starting address is '5' and No. of registers to read is '1'. This register mapping should be clearly stated in Manufacturers protocol manual. This register address 5 indicates some variable (eg: Voltage, current, power.....).

3) Write Single Coil.vi : Its a bool Input meaning you are switching something wrt Register address '9'. [This register mapping should be clearly stated in Manufacturers protocol manual.]

4) After this again you reading Holding registers 17 and 11 with same no of inputs.

Inside the Case Structure:

5) Here you are writting single Holding register : address is 11 and you are writting 2 registers. The "Numeric" gives input to the case structure. 1,2,3,4 stands for some function inside the case structure.

Note : This is not the effecient way to program. Try to learn some basics and look at some examples. Please read the modbus information here http://www.simplymodbus.ca/FAQ.htm, it simple and gives you a clear picture.

If you need any help. Send me the details i can help you.

Re: Modbus Labview Program

happinesss — Mon, 30 Apr 2018 16:18:59 GMT

Hi jay0909;

Thanks for replying. I see. Thanks for the link. I will search for that. One more thing. What is the parity(odd/even) and flow control (XON/XOFF etc.) in create serial master vi. ?

Sincerely.

Re: Modbus Labview Program

RavensFan — Mon, 30 Apr 2018 17:17:58 GMT

Flow control is probably none. But that and parity would be whatever your device says it needs to be in the manual.

Re: Modbus Labview Program

happinesss — Mon, 30 Apr 2018 22:34:53 GMT

Alright then. I will see what happens. Thanks.

Re: Modbus Labview Program

happinesss — Tue, 06 Jan 2026 21:11:07 GMT

Hi again,

I tried the program but it gives 'Error 56 occured at RTU Data Unit.lvclass:Read ADU Packet.vi:1,

Possible Reason: The network operation exceeded the user-specified or system time limit.'

I found some cases about Error 56 at discussion forum of NI, I tried some of them but they didn't give a solution. I changed the type of flow control but again each case it took the same error. I looked those pages; Error 56 when using TCP read, Error 56, NI forum Error 56 and knowledge error 56 but I couldn't solve the problem. How can I solve it?

Sincerely.

Re: Modbus Labview Program

happinesss — Tue, 01 May 2018 08:03:28 GMT

By the way, I am not communicate with the network. I am using serial connection. The problem is, I think, with the serial communication, not network but the error comes from there. I have signal converter and using com3. I checked from the device manager from the computer and it says this device working properly. I don't understand. Everything okey but there is an Error 56.

Re: Modbus Labview Program

happinesss — Tue, 01 May 2018 11:18:26 GMT

Hi again 🙂

I can successfully handled with it. I solved the problem. Here this program is for only one slave, but I have 4 slave. I want to see data on each slave and put it into a waveform chart which each of them comes from different addresses. I put the snippet below which includes the only part of the vi. Only reading the coming datas seperately. How can I find the each addresses/channels?

Sincerely.

Re: Modbus Labview Program

RavensFan — Tue, 01 May 2018 15:30:41 GMT

When you have 4 slaves, you'll have to do 4 different Modbus Reads, one with each of the slave ID's assigned to it.

Re: Modbus Labview Program

jay0909 — Wed, 02 May 2018 07:05:58 GMT

Hi,

Did you go through the protocol? Each slave has unique ID so try to communicate one by one first and then try 4 slaves. If you provide me more details i can give you my library which communicates with multiple slaves.

Re: Modbus Labview Program

happinesss — Wed, 02 May 2018 12:49:28 GMT

Hi, thanks for replies. I have 4 furnace and 1 USB/RS 485 signal converter adapter. I need to read just the data from those furnaces. Here the internet page control device of furnace and the manual . I will use four of them and need to communicate each of them separately with labview version of modbus which is exactly I showed above. Here the internet page of the signal converter that I used.

Sincerely.

Re: Modbus Labview Program

arteitle — Wed, 02 May 2018 14:07:49 GMT

You need to assign each of your controllers its own address by setting parameter 42 ("Addr", see page 18 of the manual) to a different value for each controller. Then use four Modbus read functions, one for each of the addresses you assigned. You can't perform the four reads in parallel since they all use the same RS-485 interface, so serialize them by stringing their error in/out lines together in a series. If you need more specific help than this, ask specific questions.

Re: Modbus Labview Program

happinesss — Thu, 03 May 2018 07:16:14 GMT

Hi Arteitle,

Thanks for replying. You mean like that?

Here I set the starting addresses as 1,2,3 and 4. I put those addresses to the Modbus read function as starting addresses. I think this is insufficient way?

Sincerely.

Re: Modbus Labview Program

jay0909 — Thu, 03 May 2018 10:40:20 GMT

Hi,

Can you send the whole settings mentioned on page 18 of the protocol pdf. There's a difference between starting address and slave adress.

From your previous reply:

Starting address: 5,7,11

Slave address: 1,2,3,4

Re: Modbus Labview Program

arteitle — Thu, 03 May 2018 14:55:09 GMT

As jay pointed out, the device address (more properly called the 'Unit ID") is different from the starting address (the location in the device's memory from which you want to read). The Unit ID is stored in the blue "serial master instance" wire that's wired to each of your Modbus Read functions, while the starting address is the integer that's wired to each Read. (Note, just like how you wired the error lines of the reads together in series, you should also wire the serial master instance lines between the reads in series too.) Your "New Serial Master" function has an ID of 1 wired to it, so all your subsequent reads and writes that use the serial master instance from it will talk to unit ID 1. If you want to also send queries to units 2, 3, and 4, you either need to create three more New Serial Masters with those IDs and then keep the four serial master instance wires from them separate, or perhaps easier, you can just create one Modbus Master as you have, but use the "Set Unit ID" function to change it before trying to talk to each device. You can work out how to use a For loop that repeats four times to read the same set of addresses from all four Unit IDs.

Re: Modbus Labview Program

RavensFan — Thu, 03 May 2018 19:44:17 GMT

@happinesss wrote:

Hi Arteitle,

Thanks for replying. You mean like that?

Here I set the starting addresses as 1,2,3 and 4. I put those addresses to the Modbus read function as starting addresses. I think this is insufficient way?

Sincerely.

No NO NO NO!

Like the attachment.

Don't forget to close the masters when done. Also, you need labels for your block diagram terminals like I show. You can hide the labels on the front panel if you want, but the BD should always have labels so the programmer knows what the purpose of the terminal is.

And don't use shift registers on the error wire. Not unless you do something to handle errors. Otherwise one random timeout error will cause your code to stop working until you stop and restart the VI.

Re: Modbus Labview Program

happinesss — Fri, 04 May 2018 03:13:02 GMT

Hi jay0909,

Thanks for reply. Here is the settings manuel. Yes, you are right. I saw your point and understand my wrong way. There is difference in starting address and Unit ID's which are slave ID's which I totally did it in a wrong way. As Arteitle's answer, I have easily seen my error. Again thanks. I will be more careful next time I hope 🙂 .

Re: Modbus Labview Program

happinesss — Fri, 04 May 2018 03:27:55 GMT

Hi Arteitle,

Thanks for reply. I understood what you say. Create 4 different Slave ID's, not put them in a starting address. I understood wron at first time, I thought you mean from address is that one but they are totally wrong. I have to create different IDs to communucate each slave and their whole starting address' are same. So, I can use for loop for 4 IDs or using Set Unit ID. Again, thanks a lot.

Re: Modbus Labview Program

happinesss — Fri, 04 May 2018 03:37:49 GMT

Hi RavensFan,

Thanks for reply. Sorry for weak explanations. I hope I will be more careful about the labels next time. I get your point about error. When I said insufficient, that program didn't work as expected. I can use 4 for loops as you did or I can use set unit ID in a loop as well. I understand and did the whole thing in a your way. So I think, I understand correctly. Again thanks for your efforts.

Re: Modbus Labview Program

jay0909 — Fri, 04 May 2018 07:39:49 GMT

Hi,

Can you provide me the naming convention for the registers 5,9,11,17. Because in your first post i see 9 is a coil. So can please explain what are you trying to read and write.