The ESA-721 does interpoint braille via manual interpoint. The procedure is to print odd pages first, re-thread the paper, and then print the even pages.
General Advice about Computer Ports: Serial, Parallel, USB, and Network
DIP Switches
The recommendation is to set the 8 SW1 switches as follows: off, off, off, on, off, on, off, on. These settings set North American Braille, 8 data bits, 1 stop bit.
For the SW2 switches, the first seven are off, the last switch is set on. This is for 9600 baud.
SW3 controls paper sizing.
Hardware hand-shaking generally works best.
Xon/Xoff flow control is only used on very old machines.