Interactive Connector Diagram
Click or tap any pin in the diagram below to inspect its signal assignment, electrical specification, and wire colour standard.
Supported Systems / Found On — Retro Machine Hubs
This connector is used on the following retro computer systems. Click any colour-coded badge below to open its full board-level repair, diagnostic, and schematic Machine Hub:
Connector Specifications
Full Pin Assignment & Wiring Reference
| Pin | Signal Name | Direction | Electrical Spec / Role | Wire Colour / SCART / Adapter Target |
|---|---|---|---|---|
| A1 / B1 | A1: GND | B1: SL1 (Left Audio In) | GND/In | A1: Digital GND | B1: Left Channel CD-DA + PCM Audio Input from Sega CD into Genesis mixer | B1 = Left Audio Return |
| A2 / B2 | A2: +5V | B2: AGND (Audio Ground) | Pwr/GND | A2: +5V DC | B2: Dedicated Analog Audio Ground Shield | B2 = Audio Shield GND |
| A3 / B3 | A3: VA8 | B3: SR1 (Right Audio In) | Out/In | A3: Address VA8 | B3: Right Channel CD-DA + PCM Audio Input from Sega CD into Genesis mixer | B3 = Right Audio Return |
| A4–A13 / B4–B15 | VA1 – VA23 (Address Bus) | Out | Motorola 68000 24-Bit Address Bus (VA1 through VA23) | 68000 Address Bus |
| A14 | GND (Bus Shield Ground) | GND | 0 V Bus Ground Return | Black (GND) |
| A15–A22 / B16–B23 | VD0 – VD15 (Data Bus) | I/O | Motorola 68000 16-Bit Bidirectional Data Bus (VD0 through VD15) | 68000 Data Bus |
| A23 / B24 | A23: /CAS2 | B24: /LWR & /UWR | Out | Column Address Strobe 2 & Lower/Upper Byte Write Strobes | Memory Control |
| A25 / B25 | A25: /TIME | B25: /CAS0 | Out | I/O Expansion Strobe ($A130xx) & Main ROM/RAM /CAS0 | Chip Selects |
| A26 / B26 | A26: /AS | B26: /ASEL | Out | 68000 Address Strobe (/AS) & Address Range Select ($000000–$3FFFFF) | Bus Strobes |
| A27 / B27 | A27: /CE0 | B27: /DISK | Out/In | /CE0 Chip Enable & /DISK Expansion Present Sense (Pulled LOW by Sega CD!) | B27 = /DISK Sense |
| A28 / B28 | A28: /VRES | B28: /OE0 | Out | /VRES System Reset & /OE0 Output Enable | Reset & OE |
| A29 / B29 | A29: VCLK (7.67MHz) | B29: EDCF | Out | 7.67 MHz (NTSC) / 7.60 MHz (PAL) 68000 System Clock & Bus Clock | System Clocks |
| A30 / B30 | A30: +5V | B30: GND | Pwr/GND | +5.0 V DC Supply Sense & 0 V Ground Return | Power / Ground |
Diagnosing Sega CD Detection Failures & Missing CD Audio on Model 1 vs Model 2
Located under a removable plastic cover on the right side of every Sega Mega Drive / Genesis Model 1 and Model 2 (omitted only on the budget Genesis 3), the 2×30-pin (60-contact) expansion edge exposes the full Motorola 68000 address/data bus, clock signals, chip selects, and dedicated analog stereo audio inputs (Pins B1 and B3). This allows the Sega CD / Mega-CD's own 12.5 MHz 68000 CPU, ASIC graphics scaler/rotator, and Ricoh RF5C164 8-channel PCM + Redbook CD-DA audio mixer to map directly into the Genesis memory space (`$400000–$7FFFFF` when no cartridge is present, or `$200000–$3FFFFF` alongside a cartridge).
- Genesis Boots Straight to Cartridge / Doesn't Detect Sega CD: Check Pin B27 (/DISK) and clean all 60 gold edge fingers on the Genesis side PCB with a white Staedtler Mars Plastic eraser followed by 99% isopropyl alcohol. If the Sega CD still doesn't wake up when the Genesis powers on, test continuity across fuse F301 (2.5A Pico fuse) inside the Sega CD!
- Why Mega Drive Model 1 Consoles Need the Rear Mixing Cable for Stereo Sega CD Audio: While every Genesis Model 1 and Model 2 receives stereo Sega CD audio over Expansion Pins B1 (Left) and B3 (Right) and mixes it into the front headphone jack (Model 1) and rear 9-pin Mini-DIN (Model 2), the Model 1's rear 8-pin DIN only outputs MONO! To get full stereo out of a Model 1 + Sega CD setup, run a 3.5mm TRS stereo patch cable from the Genesis 1 front headphone jack into the Sega CD's rear "MIXING" input jack, and connect your stereo amplifier to the Sega CD's rear Left/Right RCA outputs.
- MegaSD / EverDrive Pro FPGA Cartridge Audio Note: Modern FPGA flash cartridges (MegaSD, Mega EverDrive Pro) play CD-DA and MSU-MD audio without a Sega CD attached, but on an unmodded Genesis Model 1 that cartridge audio only comes out in stereo on the front headphone jack unless you solder two wires from Cartridge Slot Pins B1 & B3 to the expansion port or rear DIN.