SWD: connect a Cortex debug probe

Applies to: Five signal connections using the cited Cortex 10-pin numbering. It is not a complete 10-pin map or a map for every ST-Link clone.

When to use it

Programming or debugging a target that explicitly supports Arm Serial Wire Debug.

Why it works this way

SWD uses a bidirectional data signal and a clock, with target voltage reference and ground.

Connection reference

Make the connection

1. Use the actual probe and board connector drawings and match pin 1.
2. Power the target as documented and connect its I/O rail to VTref.
3. Select SWD and start with a conservative debug clock.

Check before powering

• VTref normally senses power; it is not permission to power the target from the probe.
• Optional SWO and unused contacts depend on the target. SWD and JTAG are different modes.

Sources & review

Source documents inspected; independent electrical and bench review pending. Reviewed 2026-09-27.

• Microchip: Cortex Debug Connector (10-pin)
  Connector drawing and SWD signal table · checked 2026-09-27
• Arm Keil: Application Note 321, version 1.1
  Page 18: five SWD connections and Cortex 10-pin numbers · checked 2026-09-27

Original writing and diagram by Kal / Valleytech Solutions, CC BY 4.0. Manufacturer artwork and documentation retain their own rights. CC BY 4.0

Continue learning

• JTAG: TCK, TMS, TDI and TDO

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