Multiple connected clients

[salasidis]

The usual code for servicing a clients only works with one connected client at a time.

while (1) {
    
    ethClient = ethServer.available();
    
    if (ethClient) {

        modbusTCPServer.accept(ethClient);

        while (ethClient.connected()) {
          modbusTCPServer.poll();

Is there a correct way (or an example) for how to connect multiple clients to the server at one time.

Thanks

[khoih-prog]

Hi @salasidis

You can try this Async eModbus library I just found out. It's designed for ESP32, but IMO, it's easy to port to other platforms, such as mbed_portenta, ESP8266, arduino-pico, , STM32, etc.

From https://emodbus.github.io/

This is a library to provide Modbus client (formerly known as master), server (formerly slave) and bridge/gateway functionalities for Modbus RTU, ASCII and TCP protocols.

Modbus communication is done in separate tasks, so Modbus requests and responses are non-blocking. Callbacks are provided to prepare or receive the responses asynchronously.

There is a synchronous interface available as well where requests are waiting for their responses to arrive.

I don't have any Modbus experience or equipment, If you'd like to try and are still interested, I can port it to multiple platforms. But you have to do all the tests.

[salasidis]

I do have a license to modbus Poll, and could buy a license for modbus server if required (from www.modbustools.com).

this is what I use to test my current project's modbus server connection. It would be willing to rewrite my code to add the use of this library to see if I can have multiple poll clients from different sites accessing the software.

I don't have any prewritten software to test the client interface, but presumably we could use the examples o test for that.

[codev123]

hi @khoih-prog , can you please port emodbus library to rp2040 arduino pico core. i will try to run tests. thank you sir

[codev123]

Hi @salasidis

You can try this Async eModbus library I just found out. It's designed for ESP32, but IMO, it's easy to port to other platforms, such as mbed_portenta, ESP8266, arduino-pico, , STM32, etc.

From https://emodbus.github.io/

This is a library to provide Modbus client (formerly known as master), server (formerly slave) and bridge/gateway functionalities for Modbus RTU, ASCII and TCP protocols.
Modbus communication is done in separate tasks, so Modbus requests and responses are non-blocking. Callbacks are provided to prepare or receive the responses asynchronously.
There is a synchronous interface available as well where requests are waiting for their responses to arrive.

I don't have any Modbus experience or equipment, If you'd like to try and are still interested, I can port it to multiple platforms. But you have to do all the tests.

sir, i can run the tests if you port the library

[codev123]

hi @salasidis , how did you connect multiple clients to connect to tcp server, please help if if were able to do that.

[salasidis]

I never did, I limited it to a single client.