The Industrial Raspberry Pi Forum

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?

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

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

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

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.

this is other screenshot pi.modbus-master status:

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

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

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

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