Hi Christian,
The firmware you’re using is for the stock WP85 module, which doesn’t have the RS485 driver.
Try loading the FX30 image from here:
source.sierrawireless.com/resou … -firmware/
R13.1.2.004 supports RS485 and you should see /dev/ttyHSL0 as well as rs_mode and rs485_term in /sys/devices…
BR,
Chris