I set up my 7300 to use with an external Zenith Z-19. You simply have to log into the "install" account and work your way to the Hardware setup window. From there find the RS232 section and if necessary change NONE to TERMINAL. I used a null modem adapter and plugged a serial cable into the RS232 port of the 7300. On the other end I plugged the serial cable into a Zenith Z-19 terminal set at 9600/N/1.
I played around with different terminal settings, settling on the VT-100 because I just wanted command line access. I got tips from vintage-computer.com to troubleshoot the signals.
Unfortunately I was not also able to get a previously untested Digital Equipment Corp VT220 to work. Not sure if it's an incompatibility with all VT220's or just this VT220 has an issue. I could receive but not send from the terminal. I did not see any activity on a diagnostic meter, so I assume for now the fault is with the VT220. I built a custom EIN box to verify I had exactly the correct wiring for a full handshaking NULL modem adapter. I don't think the signal path is the problem.
I used to work with VT220's when they were new, but I have not touched one since. Until today. This particular VT220 was lying around here for a few months, had not gotten to it yet.