Help needed with simple modbus RS485 communication to PC

[Ron]

Hi all,

Im trying to understand how to communicate through modbus RS485 with a V700 PLC.

In the end I need to connect to a blower type device but let's forget that for now (I dont have it available anyway). 

Im trying to successfully send and receive from a PC using a USB to RS485 adapter (USB to DB9 to RJ11) - DB9 pin 2 is connected to pin 1 in the RJ11 and DB9 pin 1 connected to pin 6 on the RJ11, is that correct?

Now for the program (attached):

I configure the TCP port for online view and download, then configure port 1 as RS485 with the default settings.

BTW the dipswitches are configured as a RS485 termination is that right?

Then did 1 net to read register (function 3) and 1 net to preset register (function 6), only trying to read and write 1 bit(byte?), same as would be with the blower device.

Im using a program called ComTestPro for modbus devices to try and act as the blower to read and write the first bit.

I get the following error "Incorrect function code in response", for both read and write

Does anyone know what's the problem?

any help/clues are greatly appreciated

 

TestModbus485.vlp

[kratmel]

Hi, it looks like you setup two MASTER in modbus network.

Your software, as i see offer only master function - read&write.

If you configure V700 as SLAVE via Visilogic ladder - you can read/write registers in V700 (You can find Modbus register address in Help).

Try to find software Modbus Slave emulator for use V700 as master.

[Fernando Castro]

As @kratmel modbus network should be Master(Client)-slave(Server).

Master initiates comunication and server just responds to whathever the master is asking for. 

I couldn't open your file since was developed on a newer version. Take this with with a grain of salt but I have had bad experiences with newest software versions and communications before.

So before doing anything else if I were you, I'll test communication with one of the examples on visilogic projects folder,  I suggest use morbus tcp/ipt because you already have ethernet available(as seen in that screenshot).

Just as an example, I had a perfectly working program that was released to production but when maintanance needed to install it on a machine using a brand new installation of visilogic then serial communication was not working, I rolled back the OS with my laptop using same original source project with an older version of visilogic and serial communication worked again.

Same happened a few months ago with another guy in the forum over modbus TCP/IP and a v700. 

 
 

[Ron]

On 6/7/2022 at 3:32 PM, kratmel said:

Hi, it looks like you setup two MASTER in modbus network.

Your software, as i see offer only master function - read&write.

If you configure V700 as SLAVE via Visilogic ladder - you can read/write registers in V700 (You can find Modbus register address in Help).

Try to find software Modbus Slave emulator for use V700 as master.

thanks you, I found a software to simulate slave and everything is working great!

 

On 6/7/2022 at 8:31 PM, Fernando Castro said:

As @kratmel modbus network should be Master(Client)-slave(Server).

Master initiates comunication and server just responds to whathever the master is asking for. 

I couldn't open your file since was developed on a newer version. Take this with with a grain of salt but I have had bad experiences with newest software versions and communications before.

So before doing anything else if I were you, I'll test communication with one of the examples on visilogic projects folder,  I suggest use morbus tcp/ipt because you already have ethernet available(as seen in that screenshot).

Just as an example, I had a perfectly working program that was released to production but when maintanance needed to install it on a machine using a brand new installation of visilogic then serial communication was not working, I rolled back the OS with my laptop using same original source project with an older version of visilogic and serial communication worked again.

Same happened a few months ago with another guy in the forum over modbus TCP/IP and a v700. 

 
 

Thanks for the help, didn't used it this time but defiantly keeping that in mind