The Modem or Printer Serial Port selection is at top center When using a Macintosh with a USB port, a Keyspan or Belkin USB to Serial adapter must be used. When using a USB adapter the Printer port is emulated The Videonics Command Post can be used with a USB Mac. It has 15 Buttons, a Shuttle/Jog Wheel and a Takebar Multiple V1 DDRs can be controlled with a RS-422 Mult-Box Complete Help for the Film/Vari-Speed Video™ System is always available online within the program