Is HMI STO and HMI STU series HMI can support RS 422 communication at COM1 port.
4 Wire RS-422 can be used with HMISTU and HMISTO but you need to use a cable converter HMI960. The setting should be selected as RS485 in the software for correct configuration. Basically, RS422 won't work alone with the com1 communication port. So it is further advisable that you use Modbus RS232C / RS485 protocol.