Response timeout of RTU master

[ondrej1024]

Description

I just need an information which I couldn't find in the docs. What is the default response timeout of the RTU master and how can it be changed ?

Thanks, Ondrej

Reproduction steps

None

MicroPython version

v.1.20

MicroPython board

Raspberry Pico

MicroPython Modbus version

None

Relevant log output

No response

User code

No response

Additional informations

No response

[beyonlo]

Hello @ondrej1024

Here an example https://github.com/GimmickNG/pycopy-modbus/blob/ad38bb74d2da0a4b22c518567bbee44647da7afd/examples/rtu_host_example.py#L34 where show that the default is 120 ms, and you can to change the timeout just changing the read_timeout for a new value (in ms). It works, I'm using it, changing to 200ms, 300ms, 1000 ms in my tests.

Ps1: I don't know if that works in the last version of ModBus lib because I'm using the async version #56 that will be merged soon!

Ps2: that example that I linked still is not in the official examples because the PR #56 is not finished yet.

But I agree, it is important to put in the docs what is the default timeout for the Master RTU and how to change it. Maybe @brainelectronics can to put that information in the docs when the asyncio version is merged!

[ondrej1024]

Thanks for your answer. I had a look in serial.py of the latest release 2.3.7 and found that class Serial() has no parameter read_timeout. So I guess it is not yet available and I have to wait for the merge that you mentioned to be completed.

[ondrej1024]

Do you know where the default timeout is defined? I checked the source code but couldn't find it.

[ondrej1024]

After some more digging, eventually I found the code which is responsible for the timeout.

It is in file serial.py function _uart_read() and it is determined by this loop:

        # TODO: use some kind of hint or user-configurable delay
        #       to determine this loop counter
        for x in range(1, 120):

However, the value of 120 here is not the number of ms but the number of _inter_frame_delay which depends on the baudrate. So the default timeout actually is not 120ms but depends on the baudrate. At 9600 baud it is about 500ms.