Serial Switches You can use a mechanical or electronic switch box. Mechanical switchers should work fine, allowing you to switch one of your Mac ports among three or four devices. Of course, this does not allow more than two simultaneous serial connections. Some devices, like fax modems, scanners and graphic tablets install software at Mac startup and do not like being switched without restarting the Mac. If using are considering using an electronic or automatic switcher on a PCI Macintosh, be sure to inquire with the manufacturer about compatibility with latest Apple OS software.
Macintoshes can accommodate one or more NuBus internal expansion cards.
PCI serial expansion cards 4. External via SCSI You can use a Creative Solutions SCSI-based external serial expansion unit. These add two or four ports each and appear to work reasonably well with PCI Macs. Thus this method is only practical for two to four ports at 115,200 baud or up eight ports at 38,400 baud. External via Ethernet.