Does it work on Raspberry PI Pico？

[Lyansun]

Hey buddy, how does this library work on pico？

[brainelectronics]

Hey, I haven't tested it on a Pico yet but there should not be any issues.

[AlKoAl]

Lyansun, hello. I do the same thing and I've already understood that this library isn't work on Raspberry Pi Pico without changings or adding external WiFi modules. Did you solve this problem?

Hey buddy, how does this library work on pico？

[beyonlo]

Hello @AlKoAl

What exactly do not works? Could you paste here the errors?

[AlKoAl]

Good morning, @beyonlo.

At the begining, there is no specific errors. The whole code (from main.py and boot.py) isn't working on Raspberry Pi Pico because this platform doesn't have WiFi module as well as network library among the preinstalled libraries. It definitely should work on Raspberry Pi Pico W, but i don't have it, and it will probably work on W5100S-EVB-Pico.
Modbus RTU maybe works if we comment out network library. (Working on it)

But this is not my problem to work with. I've just try to find some micropython lybrary which can give me the simplest way to develope Modbus RTU slave on this platform. My task is to create a simple transceiver, which will get the modbus commands from the higher level and control devices, such as turning on and off LEDs. (I understand, that it is usually done with microcontrollers programmed on C). Should i use UART-RS-485 transiver to create a wire connection with master? (I don't even know that. I'm frustrated.)

As I understand this library is developed to work with two devises: one will be the slave other is master which is "talking" by WiFi. (Maybe i misunderstood something.) Can I just create only slave on Rasberry and control it with for example Modscan32 (or other programs, I don't now) like you do?

[beyonlo]

This lib should be works without issues in any platform where MicroPython runs, including RPico and RPico-W

At the begining, there is no specific errors. The whole code (from main.py and boot.py) isn't working on Raspberry Pi Pico because this platform doesn't have WiFi module as well as network library among the preinstalled libraries.

You can use the this lib with ModBus RTU via serial (UART, RS232, RS485, etc) using the RPico (without WiFi or Ethernet).

It definitely should work on Raspberry Pi Pico W, but i don't have it, and it will probably work on W5100S-EVB-Pico. Modbus RTU maybe works if we comment out network library. (Working on it)

On the RPico-W (WiFi) or W5100S-EVB-Pico (Ethernet) you can use this lib with ModBus RTU and/or ModBus TCP

But this is not my problem to work with. I've just try to find some micropython lybrary which can give me the simplest way to develope Modbus RTU slave on this platform.

This project (great thanks to @brainelectronics) is the mostly simplest and amazing way to do what do you want using MicroPython.

My task is to create a simple transceiver, which will get the modbus commands from the higher level and control devices, such as turning on and off LEDs. (I understand, that it is usually done with microcontrollers programmed on C). Should i use UART-RS-485 transiver to create a wire connection with master? (I don't even know that. I'm frustrated.)

That depends what do you want. If your communication need to be RS485 for example, so you need to use ModBus RTU. But if is not necessary to use a serial communication, you can use ModBus TCP via Ethernet and/or WiFi. I think that your problem is not about this library, but to understand a bit more about network communication and about how Modbus ptotocol works. I suggest you to research about that, but I will explain a bit about this for you below.

As I understand this library is developed to work with two devises: one will be the slave other is master which is "talking" by WiFi. (Maybe i misunderstood something.)

No. You can do choose to use just the Modbus RTU Slave for example and other software can do ModBus RTU Master.

This library implement the ModBus protocol, supporting all 4 types of ModBus types:

1. ModBus RTU Slave
2. ModBus RTU Master
3. ModBus TCP Slave
4. ModBus TCP Master

So, you choose from this library what type of ModBus do you want to use. And of course, you can to use all that 4 types working together, if is what do you need.

Here a brief summary how ModBus protocol works and how these 4 types of ModBus implemention (supported by this library) works:

1. ModBus is a protocol that can run on the Serial communication and TCP communication.
2. For Serial communication, like as UART, RS232, RS485, RS422 you need to use the ModBus RTU.
3. For TCP communication, like as Ethernet and WiFi you need to use the ModBus TCP.
4. Modbus protocol has the concept of request -> response (like as the HTTP protocol) , where Slave is who wait for a request and make a response, and where the Master make the request to the Slave and wait for a response.
5. On the ModBus RTU there is a concept about Slave address, where each Slave has a specific ID (number), so the Master is capable to choose for what Slave address will make the request. So in a RS485 network for example, you can have many Slaves and just one Master, where this Master can make a request to all Slaves.
6. On the ModBus TCP, there is as well the concept about Slave address, but instead a ID number, the Slave address is just the IP address and Port that the Slave are listening. So the Master TCP need just to send a request to IP and Port where the Slave TCP is running/listening.

Can I just create only slave on Rasberry and control it with for example Modscan32 (or other programs, I don't now) like you do?

Yes

[AlKoAl]

Oh, thank you so much for such a detailed answer!
I should have asked my question earlier, you helped me a lot in organizing my thoughts. You are breathtaking! (Keanu Reeves meme)

[beyonlo]

Oh, thank you so much for such a detailed answer! I should have asked my question earlier, you helped me a lot in organizing my thoughts.

You are welcome!

You are breathtaking! (Keanu Reeves meme)

I saw that video, very good :)

[volkar1]

It doesn't work on Pi Pico W.
It will init the library class, but after you try to read holding register (for example) it will fail because machine is missing attribute 'wait_tx_done'.
It fails because of "ctrl_pin" that is needed on MAX485 chip

Full error:

  File "<stdin>", line 18, in <module>
  File "/lib/umodbus/serial.py", line 207, in read_discrete_inputs
  File "/lib/umodbus/serial.py", line 171, in _send_receive
  File "/lib/umodbus/serial.py", line 163, in _send
AttributeError: 'UART' object has no attribute 'wait_tx_done'

[AlKoAl]

It doesn't work on Pi Pico W. It will init the library class, but after you try to read holding register (for example) it will fail because machine is missing attribute 'wait_tx_done'. It fails because of "ctrl_pin" that is needed on MAX485 chip

Full error:

  File "<stdin>", line 18, in <module>
  File "/lib/umodbus/serial.py", line 207, in read_discrete_inputs
  File "/lib/umodbus/serial.py", line 171, in _send_receive
  File "/lib/umodbus/serial.py", line 163, in _send
AttributeError: 'UART' object has no attribute 'wait_tx_done'

It is true. I was traing to change the code and ctrl_pin is some of those functions that is available in this repo (it will be possible if you change the example), but "wait_tx_done" isn't available on micropython rp2040 version (but it's OK on ESP32 or ESP8266). You could try to change the function, for example to just "wait" for several miliseconds. It will work, but kinda weird. At the end i've just got problems with synchronization and droped whole idea.

[brainelectronics]

Relates to #34

[brainelectronics]

At the begining, there is no specific errors. The whole code (from main.py and boot.py) isn't working on Raspberry Pi Pico because this platform doesn't have WiFi module as well as network library among the preinstalled libraries. It definitely should work on Raspberry Pi Pico W, but i don't have it, and it will probably work on W5100S-EVB-Pico. Modbus RTU maybe works if we comment out network library. (Working on it)

good news @AlKoAl, the package has been cleaned up with version 2.0.0 and serial as well as tcp dependencies have been removed from modbus, see also https://micropython-modbus.readthedocs.io/en/2.0.0/UPGRADE.html#update-imports

[brainelectronics]

Hey @AlKoAl and @volkar1 the bug is now fixed in 2.1.2

@Lyansun you can get some more informations about the usage with a Raspberry Pi Pico in #34 and #43