The Samsung ER-650/655 has two RS-232 ports. There is not an option to add more ports.
With, an external RS-232 switch you might be able to switch devices. The port programming would need to be changed everytime you want to use the alternate device. As an example, a scale and scanner could be connected to the machine using both available ports. When you would like to have the machine communicate to a PC, you would switch one of the ports to the PC connection (direct or modem), then change the port programming, and the register could be polled. If this needed to be done on a daily basis it would be quite a headache. At that point I would think about a larger cash register with 3 or more ports.
