Yamaha MU50 Owner's Manual page 115

UTILITY MODE
About Cable Messages
The MU50 can receive Cable messages (F5) when the TO HOST terminal
is connected to the serial terminal of a computer. On the MU50, MIDI
receive channels 1 — 16 are controlled from Port 1. By connecting another
multi-timbral tone generator to the MIDI OUT terminal of the MU50 and
setting the Thru Port function (page 98) to a value other than 1, you can
play back data over a total of 32 MIDI channels — 16 on the MU50 and
another 16 on the connected tone generator.
Tone Generator
106
Thru Port setting:
2 — 8
MIDI IN
Port 1: Channels 1 — 16
MIDI
OUT
Computer and
Software with
multiple-port
capability