Trace the track from Pin 1 of the 20-pin header. Look for a small series resistor (usually 10 Ωcap omega Ωcap omega
In the world of embedded systems, a reliable debugger is as essential as a multimeter or oscilloscope. The J-Link by SEGGER is a gold standard. For many developers, the holds a special place: it marked a significant performance leap from the V8 and became a focal point for the open-source hardware community. Although SEGGER has never released its official design, the ecosystem around the J-Link V9 has produced a wealth of reverse-engineered schematics, DIY PCBs, and firmware analysis.
The hardware architecture of a J-Link V9 revolves around several key functional blocks: jlink v9 schematic
Tracing the signal flow from the USB port, through the STM32, into the level shifters, and out to the target is an excellent exercise in hardware design and digital logic. Conclusion
: Focus on the core functions you want to replicate or reference, such as USB-to-JTAG/SWD conversion, debugging capabilities, and supported microcontrollers. Trace the track from Pin 1 of the 20-pin header
Test Mode Select (JTAG) or Serial Wire Data (SWD). TCK / SWCLK: Test Clock (JTAG) or Serial Wire Clock (SWD). TDI: Test Data Input. TDO: Test Data Output. RESET: Connects to the target's reset pin. GND: Ground.
Sensing: The probe uses an internal ADC or comparative amplifier to sense the voltage on Pin 1 of the JTAG connector. For many developers, the holds a special place:
These alternatives offer modern features (USB-C, high-speed SWD, multi-drop) without legal jeopardy.
The physical interface mapped on the schematic follows the industry-standard 20-pin ARM JTAG layout. Understanding this pinout helps when tracing schematic connections to physical hardware probe points: Pin Number Signal Name Description Direct Schematic Destination Target Reference Voltage VCC of Level Shifter (Target Side) Pin 7 TMS / SWDIO Test Mode Select / Serial Wire Data Level Shifter Input/Output Pin 9 TCK / SWCLK Test Clock / Serial Wire Clock Level Shifter Input Pin 5 Test Data In Level Shifter Input Pin 13 Test Data Out / Trace Output Level Shifter Output Pin 15 Target System Reset (nRESET) Open-drain Buffer / Transistor Pin 19 V50-SUPPLY Optional 5V Supply to Target PTC Fuse / MOSFET Switch Pins 4-20 (Evens) Common Ground System Ground Plane 4. Common Troubleshooting and Repair Using the Schematic
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