The ESA-721 does interpoint via manual interpoint (print odd pages first. rethread the paper. and then print the even pages.
General Advice about Computer Ports: Serial. Parallel. USB. and Network
It looks like SW1 should be off off off on off on off on. This sets North American Braille. 8 bits. 1 stop bit
It looks like SW2 should be seven switches off. last switch on for 9600 baud
SW3 is for paper sizing.
Our experience is that hardware hardshaking works best. Xon/Xoff flow control is really only used on very old machines.