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.
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
QL SER1 (DCE)
Pin 1=GND, Pin 2=RXD In, Pin 3=TXD Out, Pin 4=CTS In, Pin 5=DTR Out, Pin 6=+12V DC Out!
QL SER2 (DTE)
Pin 1=GND, Pin 2=TXD Out, Pin 3=RXD In, Pin 4=DTR Out, Pin 5=CTS In, Pin 6=+12V DC Out!
QL-NET Jacks
Dual 3.5mm Mono Jacks (Tip = Scout/Data 100kbps, Sleeve = GND) — daisy-chains up to 64 QLs & ZX Spectrums!
Full Pin Assignment & Wiring Reference
| Pin | Signal Name | Direction | Electrical Spec / Role | Wire Colour / SCART / Adapter Target |
|---|---|---|---|---|
| 1 | GND (0 V Signal Ground) | GND | 0 V Signal Ground on BOTH SER1 and SER2 (Connect to PC DE-9 Pin 5!) | PC DE-9 Pin 5 (GND) |
| 2 | SER1: RXD In | SER2: TXD Out | I/O | SER1: Receive Data In (to PC Pin 3 TXD) | SER2: Transmit Data Out (to PC Pin 2 RXD) | SER1->PC 3 | SER2->PC 2 |
| 3 | SER1: TXD Out | SER2: RXD In | I/O | SER1: Transmit Data Out (to PC Pin 2 RXD) | SER2: Receive Data In (to PC Pin 3 TXD) | SER1->PC 2 | SER2->PC 3 |
| 4 | SER1: CTS In | SER2: DTR Out | I/O | SER1: Clear To Send Input (to PC Pin 7 RTS) | SER2: DTR Handshake Output | Handshake |
| 5 | SER1: DTR Out | SER2: CTS In | I/O | SER1: DTR Handshake Output (to PC Pin 8 CTS) | SER2: Clear To Send Input | Handshake |
| 6 | +12.0V DC OUTPUT (DANGER!) | Pwr | +12 V DC Auxiliary Supply Output — LEAVE COMPLETELY UNCONNECTED IN PC CABLES! | DO NOT CONNECT! |
| 7, 8, 9 | NC / Boot Select | NC | Leave Unconnected | NC |
Wiring a Sinclair QL SER1 to PC 9-Pin (DE-9) Transfer Cable
Designed in 1983 before IBM introduced the 9-pin PC AT serial pinout (1984), the Sinclair QL uses two 9-pin D-Sub sockets (SER1 and SER2, driven by the ZX8302 ULA and 8049 IPC) with Sinclair's own pin assignment — where SER1 is wired as DCE (Modem) and SER2 is wired as DTE (Terminal/Printer), swapping Pins 2/3 and 4/5 between the two sockets!
- To connect Sinclair QL SER1 to a modern PC USB-to-RS232 9-pin adapter: Wire QL SER1 Pin 1 (GND) -> PC Pin 5 (GND), QL SER1 Pin 2 (RXD In) -> PC Pin 3 (TXD Out), QL SER1 Pin 3 (TXD Out) -> PC Pin 2 (RXD In), QL SER1 Pin 4 (CTS In) -> PC Pin 7 (RTS Out), and QL SER1 Pin 5 (DTR Out) -> PC Pin 8 (CTS In). Leave QL Pin 6 (+12 V) completely disconnected!