The TS-4200 brings out 7 UARTs at 0-3.3V levels, but typically the baseboard will include transceivers to bring this to RS232, RS485, or RS422. You can find resources for programming with serial ports in Linux here:
When ttyS1 is connected to an RS485 transceiver the FPGA can be configured to autmoatically toggle TX Enable. This uses the FPGA to assert TXEN when transmitting and deassert when not. You can enable this by toggling a register in the #Syscon:
# Enables auto TX Enable in FPGA for ttyS1 peekpoke 16 0x3000000A 0x756
For UART4 (ttyS5) you will need to toggle the TX enable FPGA DIO14 manually.