Hi @TobidieTopfpflanze ,
I would say that there might be issue with the setup of minicom. You can install cutecom and run sudo cutecom to test with the loopback (Tx shorted to Rx). For example, following is the configuration of THS2 (without any HW handshaking) :
By default both following uarts work without any modification in dtsi/dts :
[ 1.563865] 3100000.serial: ttyTHS0 at MMIO 0x3100000 (irq = 47, base_baud = 0) is a TEGRA_UART
[ 1.565110] 3110000.serial: ttyTHS1 at MMIO 0x3110000 (irq = 48, base_baud = 0) is a TEGRA_UART
Note that the Tx and Rx of ttyTHS0 (3100000) is mapped to pin 203/205 of the Xavier NX SOM, Tx and Rx of ttyTHS1 (3110000) is mapped to pin 99/101.
Regards,
K