The SEGGER J-Link is a USB-powered JTAG emulator that connects via USB to a PC and via JTAG/SWD to the target system. J-Links are compatible with various CPU cores including ARM, RISC-V, and others, making them versatile debug probes.
The J-Trace is an extension of the J-Link that adds real-time trace capabilities, allowing for more advanced debugging features and performance analysis.
* Pins marked with GND* are Ground on most debuggers but may be used for other purposes in some special adapters.
| Pin | Name | Description |
|---|---|---|
| 1 | VTref | Target reference voltage. Used to check if target has power and as reference for input comparators. |
| 2 | NC | Not connected. Reserved for compatibility. |
| 3 | nTRST | JTAG Reset. Output from J-Link to the Reset signal of the target JTAG port. |
| 4 | GND | Ground |
| 5 | TDI | JTAG data input of target CPU. |
| 6 | GND | Ground |
| 7 | TMS | JTAG mode set input of target CPU. |
| 8 | GND | Ground |
| 9 | TCK | JTAG clock signal to target CPU. |
| 10 | GND | Ground |
| 11 | RTCK | Return test clock signal from the target. |
| 12 | GND | Ground |
| 13 | TDO | JTAG data output from target CPU. |
| 14 | GND* | Ground |
| 15 | nRESET | Target CPU reset signal (active low). |
| 16 | GND* | Ground |
| 17 | DBGRQ | Debug request. Not connected in J-Link. |
| 18 | GND* | Ground |
| 19 | 5V-Supply | Can be used to supply power to the target hardware (max. 300mA). |
| 20 | GND* | Ground |