The Industrial Raspberry Pi Forum

Dear Dirk,

I am currently using a RevPi Connect 5 configured as a Modbus RTU slave, while a Raspberry Pi 5 acts as the Modbus master, connected via USB RS485 to the X2 RS485 expansion port on the RevPi.

I have followed all available instructions to enable the RS485 terminal function on the RevPi, including building and running the C program that toggles the SER_RS485_TERMINATE_BUS flag. However, the /dev/ttyRS485 device does not appear on my RevPi. The only available serial device is /dev/ttyAMA10.

Despite configuring the Modbus device in PiCtory and mapping IO channels correctly (e.g., to DIO modules), the RevPi does not respond to Modbus RTU messages sent from the Raspberry Pi 5. A multimeter test also shows that the 120Ω termination resistor is not active, suggesting that the RS485 bus is not properly enabled on the X2 port.

I am confident that the wiring, PiCtory configuration, and register mappings are correct. However, attempts to communicate over RS485 consistently result in no response from the RevPi (timeout errors on the master side).

If you have:

Official documentation to enable and validate the X2 RS485 port,

Any steps or kernel configurations to ensure the RS485 device shows up correctly (e.g., /dev/ttyRS485),

Or example code or working configurations for RevPi Connect 5 RS485 slave setup,

…I would be very grateful if you could share them. I appreciate your time and look forward to any assistance you can provide.

Hi

you you please share the output of

• ls -l /dev/ttyAMA*
• ls -l /dev/ttyRS485*
• cat /etc/revpi/image-release
• ls -l /lib/udev/rules.d/50-revpi.rules
• md5sum /lib/udev/rules.d/50-revpi.rules