RevPi connect 5 RS485 - 3964R

[miko]

Hello everyone,

I have a large device that I don't have the liberty to describe here but I am sure that it has the ability to communicate / exchange messages following RS485/3964R implementation (fun fact, validated with a raspberry pi with a RS485 usb dongle). I have tested "low level" approaches with stty and python/pyserial approaches that work perfectly.

I have a RevPi connect 5. I can exchange serial messages with the same usb dongle (RS85 converter) plugged in the revpi, but absolutely impossible to make it work with the RS485 port that is on the "top right" of the module. I have triple checked the reference, the cables, all the configurations I could possibly imagine, nothing works. I have a strong feeling that there is something that is blocking the usage of the port a the software level.

We are losing days on the implementation on site of a large production system because of that, any help would be really appreciated.

Many thanks

[tboehler]

Hi miko. The Connect 5 comes in multiple variants, one of which doesn't have a RS485 interface but has a CAN interface in its place instead. Can you give a little more detail on how you are trying to access the interface on your Connect 5? What behaviour are you observing when using the interface?

Here is our documentation on the RS845 interface on the Connect 5: https://revolutionpi.com/en/docs/revpi- ... _interface

[miko]

Hello thank you so much for taking the time.

We have the 100419 item number - so from what I get on the website, we should have a working RS485.

I have the following test configuration:
- The RS485 port three wires (N, P and GND) of the revPI connected to a generic RS485 usb dongle (and I know it works in other settings).
- This usb dongle is connected to an old raspberry pi 3 (just for debugging purposes) to read messages sent by the revpi connect 5.

Nothing, with respect to rs485 is configured in pictory.

On all the machines, I have configured the RS communication as follow :

Code: Select all

stty -F /dev/ttyRS485 9600 cs8 -cstopb parenb -parodd -ixon -ixof -crts cts

And then use regular bash commands and user inputs to send / receive messages. The very same inputs work with other hardware.

Is it clarifying ? I am having the feeling that something is off in terms of software configuration, looks like the serial port is locked by an other process maybe ?.

[miko]

I forgot, the behavior is that I can't see an STX or any other character when I send them.

[tboehler]

Hi miko, thanks for the information! At first glance I can see that the parameters to the "stty" command you posted are wrong, namely "-ixof" should be "-ixoff" and "-crts cts" should be "-crtscts", otherwise the "stty" command fails.

Once I fixed this I tried it out and couldn't reproduce your problem on my test setup; a Connect 4 with a RS485 USB dongle connected to a Connect 5. Both sides set their respective RS485 device with the following command, shown here for the Connect 5:

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sudo stty -F /dev/ttyRS485-0 9600 cs8 -cstopb parenb -parodd -ixon -ixoff -crtscts

I can send a message from the Connect 5 and the Connect 4 receives it without issues. This also works the other way around.

Connect 5 sends:

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$ echo "test" | sudo tee /dev/ttyRS485-0
test

Connect 4 receives:

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$ cat /dev/ttyUSB0
test
^C

On a standard RevPi image there also isn't a process taking control of the RS485 device so it should be free to use. By the way, the "/dev/ttyRS485" symlink was deprecated with bookworm and will be removed with trixie, so make sure to use "/dev/ttyRS485-0" instead.

Sadly I cannot seem to reproduce the issue. You said you already checked everything, but can you check again that the cables are properly connected to the correct screw terminals, i.e. the polarity is correct?

[miko]

Hi tboehler,

Yes sorry for the typos in the command line, I prepped something at home, fixed it on site and did the copy/paste on the wrong version of the document. All that to say we used the very same command.

Ok - so there should not be anything that is blocking the connexion or alike, good to know. At least I won't be chasing suspicions about something I don't know about (we have not changed the pre-installed os).

I will give it a new round asap during the week (I can't go on the site that freely) with your exact commands. In the first few tests, I did reverse the wires, just in case, nothing changed. Maybe I will spot something that I missed next time around.

Once I get it to work with stty, I know it won't a problem with the high-level scripts, but as long as this is not working, I am basically stuck.

I will share updates when I have them, it is not an option for me to not have it working.


Many thanks for your support.