No such file or directory: '/dev/ttyRS485'

[MikeStern]

Hi,
i have a communication problem with Modbus RTU communication on MyrevPi Connect +.
The communications are working well but, a few hours ago, I had this problem when I launch my Python program (influxDB.py) to read the modbus RTU data from my device. Now not found !
I use minimalmodbus driver (https://minimalmodbus.readthedocs.io/en/stable/) to read directly via mudbus RTU.
This is th error:
No such file or directory: '/dev/ttyRS485'

Terminax


Configuration


Can someone help me?

[nicolaiB]

Hi Mike,

if it worked before then there might be an error with the USB UART which provides the RS485 interface on the connect. Is there anything suspicious in the kernel log (/var/log/kern.log)?

-Nicolai

[MikeStern]

Hi Nicolai
I'll send you the Kernel Log tomorrow.

Other useful information about my problem:
if i use '/dev/ttyUSB0' (with usb/rs485 adapter) all work correctly !!!
[/u]if i use '/dev/ttyRS485' (with two wire +- connected to modbus rs485 pinout) doesn't work !!!
Also the command piTest -r Modbus_Master_Status return error 255.

Thanks

[nicolaiB]

Hi Mike,

if you want to use the RS485 Interface with minimalmodbus (other other 3rd party libs), you make to make sure that PiModbusMaster / Slave are not activated on this interface. Otherwise the communication will fail / break / do unpredictable things.

-Nicolai

[MikeStern]

Hi Nicolai,

this is the kernel.log:


Slave option is disabled:


is there any system bug on the RS485 port that needs updating?

I need urgent assistance because we are buying 50 pcs (for our monitoring system) but we are worry by this error.

Thanks.

[MikeStern]

this is other screenshot pi.modbus-master status:

[nicolaiB]

Can't see anything about your interfaces in the kern.log. Is `dmesg` maybe a bit verboser on your system?

Btw: From your screenshots I can see that you're using a quite old image on your RevPi's (at least Stretch, with Buster we changed the colours to orange). Is there any special reason to this? If not I would highly suggest to update to the latest Buster Image.

-Nicolai

[MikeStern]

Hi Nicolai,
Yes on my device there is Stretch (no particolar reasons, but only because i had buy this device 24 months ago').
I have to update to Buster

[MikeStern]

Hi Nicolai,

i had update ro Buster the revPi and seems to be ok, but now i have this problem via SSH " Server does not support diffie-hellman-group1-sha1 for keyexchange"
How i can solve it?:



Thanks

[nicolaiB]

Hi Mike,

diffie-hellman-group1-sha1 is a old and deprecated keyexchange algorithm. Please check in clients SSH config why it tries to use it. Usually a SSH client auto negotiates keyexchange algorithm with the server and use a recent one. This thems to be disable in your SSH client.

-Nicolai