MIDI (Musical Instrument Digital Interface) is a protocol that allows computers, synthesizers, sound cards and drum machines to control each other and to exchange system information.

Physically, it's an one-way (simplex) serial current-loop connection running at 31,250 bits per second and it requires five-pin DIN plugs for MIDI-IN, MIDI-OUT and occasionally MIDI-THRU.

There are many MIDI Interfaces for the MSX computers, most of them are external cartridges, but some machines have a built-in interface.

MSX computers with MIDI interface

Name	Ports	UART	Remarks
Panasonic FS-A1GT	In, out	Intel i8251 + i8253	Internal MSX-MIDI
Yamaha CX5	In, out	Yamaha YM2148	Side-slot module SFG-01
Yamaha CX5F	In, out	Yamaha YM2148	Side-slot module SFG-01
Yamaha CX5M	In, out	Yamaha YM2148	Side-slot module SFG-01
Yamaha CX5MII	In, out	Yamaha YM2148	Side-slot module SFG-05
Yamaha CX7M-128	In, out	Yamaha YM2148	Side-slot module SFG-05
Yamaha CX11	In, out	Yamaha YM2148	Side-slot module SFG-01

MSX peripherals with MIDI interface

Name	Type	Ports	UART	Remarks
Bit² MIDI Interface Cartridge BM-012	cartridge	In, out, thru	Toshiba SoC with build in Z80	AKA "MIDI-Saurus"
Bit² μ.Pack BM-117	cartridge	In, out	Intel i8251 + i8253	External MSX-MIDI
FAC MIDI Interface	cartridge	In, out	Intel i8251	Timing by 4MHz crystal with some logic chips
Harukaze	cartridge	In, out	16550A/B/C, 16552A/B/C, 16750 or 16752	It's an RS-232 interface by default. To play MIDI, it must have been built with the optional MIDI mode
JoyMIDI	adapter cable	Out	None	Connects to joystick port, programmed via bitbanging
JVC MSX MIDI Interface	cartridge	In, out (x2), din clock/start/stop	Motorola MC68B50
NHK NSFG-05	proprietary cartridge	In, out	Yamaha YM2148	Identical to Yamaha SFG-05
Philips NMS 1205 Music Module	cartridge	In, out, thru	Motorola MC68B50
Tada MIDI cable	adapter cable	Out	None	Connects to printer port, programmed via bitbanging
WORP3/SuperSoniqs MIDI-PAC	cartridge	Out		Redirects PSG and MSX-MUSIC musics to MIDI in real time
Yamaha SFG-01	proprietary cartridge	In, out	Yamaha YM2148	MBIOS 1.0 does not support MIDI interrupts. The hardware itself does, though.
Yamaha SFG-05	proprietary cartridge	In, out	Yamaha YM2148
Yamaha SMD-01	proprietary cartridge	In, out, thru	Yamaha YM2148 + i8253-5