Neo Geo Pocket Color Link Cable

Full pinout, null-modem crossover, and serial protocol of the Neo Geo Pocket Color link cable (works on the mono Neo Geo Pocket too) — undocumented for 25+ years, reversed end to end and confirmed three independent ways. Play it linked online: lude.rs/ngp-link.

• Physical capture — a logic analyzer on the mainboard records real two-console traffic.
• Static disassembly — the ROM decompiled (TLCS-900/H) for the state machine, BIOS ABI, framing.
• Dynamic emulation — the real ROM executed, its output matched to the wire.

The link

Wiring	passive null-modem crossover (GND straight, TXD↔RXD, /CTS↔/RTS); no active parts
Line	19200 8N1, 3.3 V CMOS, LSB-first, idle-high, CTS/RTS — TMP95C061 SIO0
Model	lockstep ~33.4 ms (~30 Hz), P1 (FC requester) ⇄ P2 (FD responder)

Protocol at a glance

0xF_ bytes are control tokens; everything else is payload.

Phase	Wire
Handshake	FC 01 00 30 ⇄ FD 01 00 30
Transport	F0–F7 control (phase / event / payload)
Gameplay	F8 00 <P2> offer / F8 <P1> <P2> reply
Teardown	F8 FE FE, standalone FE, FF

Add it to your emulator: implementer's guide.

Scope

Reversed from Samurai Shodown 2. The framing is BIOS-level and works on mono NGP and color NGPC alike; only catalog values (e.g. 0x0030) are per-game.