Interactive JTAG & SWD Wiring Guide

Common Use Cases & Examples

This tool helps you avoid wiring mistakes and potential damage by generating clear, correct debug wiring tables.

Connect an ST-Link to an STM32 board

Select ARM 10-pin Cortex Debug as the target and ST-Link/V2 (or V3) as the debugger. Use the Minimal SWD filter to show the essentials: SWDIO, SWCLK, GND, VTref (+ nRESET recommended).

JTAG pinout for a generic ARM board

Choose ARM 20-pin Standard JTAG as the target and Segger J-Link (20-pin) as the debugger. You’ll see TMS, TCK, TDI, TDO, nTRST, nRESET, and more.

Using a Raspberry Pi Pico as a debugger

Pick your target connector (e.g., MIPI-10/Cortex-10 or TC2050) and choose Raspberry Pi Pico (Picoprobe) as the debugger. Defaults are GP2=SWCLK, GP3=SWDIO. UART for VCP commonly uses GP4/GP5 (can be changed).

Signal Descriptions

JTAG vs. SWD

JTAG uses 4–5 lines (TMS, TCK, TDI, TDO, nTRST). SWD is a 2-wire alternative (SWDIO, SWCLK). Probes usually support both; pins are often multiplexed.

⚠️ Voltage Reference (VTref)

VTref is a probe input: it tells the probe the target I/O level. Do not power the target via VTref and avoid series resistors here. On ARM-20, pin 19 may provide +5 V from some probes—use with care.