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[smilesdavis]

Macintosh Serial MIDI: Hardware, Cables, Clocking, Protocols and Drivers
Mac hardware → connector → cable topology → clock source/rate → serial data rate/framing → virtual-port framing → driver/API

1984–1990 — Macintosh serial hardware

• Macintosh 128K / 512K / 512Ke: Zilog Z8530 SCC; separate modem/printer channels; DE-9 Macintosh differential serial; fewer handshake/clock connections than later Mini-DIN-8.
• Macintosh Plus (1986): Mini-DIN-8 serial; Tx± / Rx± / HSKi / HSKo; HSKi = handshake input or external SCC clock; GPi pin 7 not connected.
• SE / Macintosh II generation (1987–): Mini-DIN-8 becomes standard; two SCC channels = modem + printer. SE/SE30/II-family/Portable modem-port GPi provides additional SCC clock routing; LC, like Plus, has GPi pin 7 unconnected.
• Apple System Peripheral-8 Cable M0197 (1987): straight Macintosh Mini-DIN-8 peripheral cable later specified by Yamaha TG100 and Opcode Studio 5.
• Mac serial hardware supports asynchronous, synchronous and externally-clocked operation where the required SCC clock paths are exposed.

1991

• Yamaha TG100: external 1 MHz clock → Mac HSKi; 8-bit / 1 stop / no parity; MIDI Time Piece = OFF; Apple System Peripheral-8 Cable M0197.

1992

• Opcode Studio 5: Apple System Peripheral-8 equivalent serial cable; MIDI Time Piece emulation.

1993

• Centris 660AV / Quadra 840AV: GeoPort introduced on modem port; 9-pin circular socket accepts Mini-DIN-8 plugs; pins 1–8 retain Macintosh serial signals; pin 9 supplies GeoPort power; synchronous/DMA functions added.
• Roland RSC-15APL family: Mac COMPUTER connection; 1 MHz; straight-through Mini-DIN-8 ↔ Mini-DIN-8 wiring.
• Kawai K11: direct Mac serial; 1 MHz.
• E-mu SoundEngine: sound module + Macintosh MIDI interface; Mac can address sound module, MIDI interface or both; supplied Mini-DIN-8 Mac cable; printer/modem thru; dedicated MIDI-interface routing mode.
• Opcode Studio 4: interoperates with MTP but uses a different, more efficient host protocol.

1994

• Power Macintosh 6100 / 7100 / 8100: Macintosh serial survives the 68K → PowerPC transition; modem/printer serial remains available to existing MIDI hardware.
• PowerBook 500 series: one external Macintosh serial port rather than separate printer + modem connectors.

1995

• PowerBook 190 / 5300: one Mini-DIN-8 Macintosh serial port; LocalTalk remains supported.
• Yamaha MU50: Standard MIDI Interface; 1 MHz; F5 Cable Messages: Port 1 = internal 16 channels; Thru Ports 2–8.
• Korg X5DR: AG-002; serial data = 31.25 kBPS; application clock = 1 MHz; KORG MIDI Driver; KORG PCIF / 1 MHz modes; KORG PCIF exposes separate Synth Out / MIDI Out; 1 MHz mode combines internal TG + MIDI OUT; F5 00/01/02 line-control commands; KORG MIDI Driver inserts required control messages.

1996

• PowerBook 1400: one standard Mini-DIN-8 Macintosh serial port; synchronous / asynchronous / AppleTalk; HSKi / HSKo / GPi / Tx± / Rx±.
• Generalmusic WK4: direct Mac COMPUTER connection; standard Mac serial cable; 1 MHz; COMPUTER port = Group A / 16 MIDI channels only.
• Alesis QS/QSR: direct Mac serial; MAC 1 MHz; QS pin 1 = 1 MHz → Mac pin 2; Mac uses bit-clock handshake to determine baud rate.
• MOTU MIDI Timepiece AV: 8×8 Mac/PC MIDI interface; Mac serial; MTP networking.

1997

• Power Macintosh G3 Beige: printer/modem Macintosh serial retained; final desktop Power Mac generation with factory legacy serial ports.
• Yamaha MU100: MIDI Time Piece = ON for 32 parts; 1 MHz; F5 Cable Messages: Port 1 = A1–A16; Port 2 = B1–B16; Thru Ports 3–8; 32 channels over one serial cable.
• Korg NS5R: AG-002B; BPS Select = 31.25; application clock = 1 MHz; no KORG PC IF; KORG / Apple MIDI Driver; F5 01 = MIDI OUT; F5 02 = Port A; F5 03 = Port B; F5 xx = line-control bytes, not legal MIDI messages.
• Emagic Unitor8 family: MTP emulation; 1 MHz / FAST; F5 xx “cable messages”; format compatible with MOTU MIDI Time Piece; Port 0 = MTP Cable 0 / send to all; LocalTalk / MIDI Time Piece / MIDI Express serial cables usable.

1998

• PowerBook G3 Series / Wallstreet: 9-pin Macintosh serial/GeoPort socket accepts 8- or 9-pin plugs; asynchronous or synchronous operation up to 4 Mbps; AppleTalk + GeoPort protocols; HSKi = handshake input / external clock up to 4 Mbps.
• iMac G3: external Macintosh serial and ADB removed; USB takes their place.
• Serial replacement problem: generic serial compatibility does not guarantee Macintosh SCC clock compatibility.
• Unitor8 replacement-port tests: Griffin iPort ❌ / KeySpan USB Serial Adapter ❌ — no external-clock option; GeeThree Stealth ✅ / Griffin gPort ✅ — modem-port compatible; FAST + AMT.
• Griffin iPort: despite failing the Unitor8 external-clock requirement, works with other serial MIDI interfaces; tested through Opcode Studio 5.

1999

• Power Macintosh G3 Blue & White: no factory Macintosh serial; USB + FireWire; serial MIDI requires USB or PCI replacement hardware.
• PowerBook G3 Lombard: external Macintosh serial removed; USB replacement era.
• Technics SX-PX332: SZ-JJAP1 Mac cable; COMPUTER port; MIDI-interface clock = 1 MHz.
• Midiman BiPort 2x4s: Mac printer/modem serial; 2 MIDI In / 4 Out; OMS; BiPort OMS driver.
• Keyspan SX Pro: 4× RS-422 Mini-DIN-8; up to 1 Mbps; MIDI support; printer-port emulation.
• MegaWolf Romulus/Remus: PCI serial MIDI via FreeMIDI; DP 2.5.1 ✅, LAP 3.7.2 ✅, Cubase VST 4.0 ⚠, Vision ❌.

Protocol evolution / observations

• Yamaha: TG100 = external-clock transport / MTP OFF → MU50 = F5 cable/port layer → MU100 = two F5 ports / 32 parts + MTP configuration.
• F5: Yamaha, Korg and MTP-compatible implementations use an F5 host-control/cable layer; shared F5 usage ≠ proven protocol identity or interoperability.
• Opcode: Studio 5 offers MTP emulation; Studio 4 interoperates with MTP while using its own more efficient host protocol.
• Emagic: Unitor8 offers MTP emulation while retaining FAST / AMT operation.
• Protocol identity ≠ compatibility mode: Opcode and Emagic can present an MTP-compatible personality without their native protocol being MTP.

Bottom line:

same Mini-DIN-8 connector ≠ same cable
same cable ≠ same host protocol
1 MHz clock ≠ serial data rate or MTP
GeoPort hardware ≠ GeoPort protocol
F5 xx = virtual-port / line-control framing, not proof of protocol identity
MTP compatibility may be emulation rather than native protocol identity
USB serial ≠ Macintosh SCC
replacement-port compatibility = electrical/clock support + port emulation + driver/API

❓ Remaining byte-level questions:

F5 mapping/interoperability: Yamaha/Korg ↔ MOTU MTP
MOTU FAST + network framing
Opcode native host protocol
Midiman serial host protocol