Interactive Connector Diagram
Click or tap any pin in the diagram below to inspect its signal assignment, electrical specification, and wire colour standard.
Click any pin to view its signal assignment, electrical spec, and wire colour.
Used in Retro Machine Hubs
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Connector Specifications
Plus/4 Square DIN
4-Pin Square DIN (No center pin! Pin 1=+5V, Pin 2=GND, Pins 3&4=9V AC)
C16 / C116 Barrel
5.5×2.1mm Barrel Jack — 9.0 V DC @ 1.0–1.5 A, CENTRE-NEGATIVE (Tip = GND)
ZX Spectrum Barrel
5.5×2.1mm Barrel Jack — 9.0 V DC @ 1.4–2.0 A, CENTRE-NEGATIVE (Tip = GND)
Full Pin Assignment & Wiring Reference
| Pin | Signal Name | Direction | Electrical Spec / Role | Wire Colour / SCART / Adapter Target |
|---|---|---|---|---|
| Plus/4 Pin 1 (Top-Left) | +5.0V DC | Pwr | Plus/4 Regulated +5.0 V DC Supply (viewed looking into male PSU plug) | Red (+5V DC) |
| Plus/4 Pin 2 (Bottom-Left) | GND (0 V) | GND | Plus/4 0 V DC Digital Return Ground | Black (GND) |
| Plus/4 Pin 3 (Top-Right) | 9.0V AC (1) | Pwr | Plus/4 9.0 V AC Transformer Winding Leg 1 | Yellow (9V AC) |
| Plus/4 Pin 4 (Bottom-Right) | 9.0V AC (2) | Pwr | Plus/4 9.0 V AC Transformer Winding Leg 2 | Yellow (9V AC) |
| C16/ZX Barrel INNER TIP | GND (0 V NEGATIVE!) | GND | C16, C116 & ZX Spectrum: Inner Center Pin is 0 V NEGATIVE! | Black / White Stripe (Tip = -) |
| C16/ZX Barrel OUTER SLEEVE | +9.0V DC POSITIVE! | Pwr | C16, C116 & ZX Spectrum: Outer Metal Barrel is +9.0 V DC POSITIVE! | Red (Outer = +9V) |
Building a C64-to-Plus/4 Adapter & Using Guitar Pedal PSUs on C16 / Spectrum
While the Commodore Plus/4 uses a 4-pin Square DIN (electrically identical to a C64 power supply: +5 V DC @ 1.5 A + 9 V AC @ 1 A), the cost-reduced Commodore 16 and C116 — just like the Sinclair ZX Spectrum 16K/48K/128K/+2 — use an external 9 V DC wall wart with a CENTRE-NEGATIVE barrel plug feeding an internal 7805 regulator.
- C64-to-Plus/4 Power Adapter Cable: Wire a 7-pin Female DIN socket (connected to any modern C64 PSU) to a 4-pin Square DIN Male plug: C64 Pin 5 (+5V) -> Plus/4 Pin 1; C64 Pins 1/2/3 (GND) -> Plus/4 Pin 2; C64 Pins 6 & 7 (9V AC) -> Plus/4 Pins 3 & 4.
- Safe Modern 9V Centre-Negative Supply for C16, C116 & ZX Spectrum: High-current 9V DC centre-negative supplies designed for Boss/Strymon guitar pedals (1.5 A to 2.0 A, low-noise regulated 9.0 V DC, 5.5x2.1mm centre-negative) are a 100% plug-and-play match!