Owner's Manual
Page 110
... connection cable, use a special MIDI cable. Set the HOST SELECT switch on the MIDI interface to the MIDI IN terminal of the PSR-550, as shown in the application software to a computer and take advantage of the wide range of the PSR-550. Connecting to a Personal Computer Connect your computer features a USB interface, we recommend using the Yamaha UX256.
... connection cable, use a special MIDI cable. Set the HOST SELECT switch on the MIDI interface to the MIDI IN terminal of the PSR-550, as shown in the application software to a computer and take advantage of the wide range of the PSR-550. Connecting to a Personal Computer Connect your computer features a USB interface, we recommend using the Yamaha UX256.