The next system with RS-232 support:

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]
[Linked Image from i.imgur.com]

Also made slots of all the things:

Code
 SYSTEM      SLOT NAME    SLOT OPTIONS    SLOT DEVICE NAME
----------  -----------  --------------  ----------------------
vz300        io           joystick        Laser/VZ Joystick Interface
                          printer         Laser/VZ Printer Interface

             mem          disk            Laser/VZ Floppy Disk Controller
                          laser110_16k    Laser 110/200/VZ-200 16k Memory
                          laser210_16k    Laser 210/VZ-200 (DSE) 16k Memory
                          laser310_16k    Laser 310/VZ-300 16k Memory
                          laser_64k       Laser/VZ 64k Memory
                          rs232           DSE VZ-200/300 RS-232 Interface
                          wordpro         DSE VZ-300 WordPro