A note on the AMS1117‑3.3: its dropout voltage is about 1.1 V at full current. If the USB supply drops to 4.4 V (the lower limit of the USB specification), the output may become unstable. For this reason, good PCB designs provide a solid ground plane under the regulator to help with heat dissipation.
Many hobbyists use the J-Link V9 schematic to repair "bricked" units. By identifying the on the schematic, you can use another working debugger to reload the bootloader onto a dead J-Link.
The 20-pin header follows the ARM JTAG standard. Key pins include: Target Voltage Reference (senses the target voltage). SWDIO/TMS ( ): Serial Wire Data I/O. SWCLK/TCK ( ): Serial Wire Clock. GND ( ): Ground. RESET ( ): Reset signal. E. Power Management and Protection
I can provide target pin maps, bootstrap procedures, or component values tailored to your specific project needs. Share public link jlink v9 schematic
differential impedance of the USB cable, preventing signal reflections.
: Allows the debugger to perform a hardware reset on the target chip. J-Link Interface Description - SEGGER
A complete J‑Link V9 schematic typically includes devices to handle: A note on the AMS1117‑3
The 20-pin standard JTAG/SWD connector brings the (Target Reference Voltage) signal from the target board. This voltage is used to dynamically set the logic levels of the debug signals. A popular choice for this level shifting is the SN74LVC2T45 , a dual-bit, dual-supply bus transceiver. It has a "VccA" side connected to the J-Link's internal 3.3V and a "VccB" side powered directly by the target's VTref. This ensures that the signals on both sides always swing to the correct full voltage levels.
The Segger J-Link is arguably the most ubiquitous family of debug probes in embedded systems development. Supporting thousands of microcontrollers (ARM Cortex-M, RISC-V, Renesas RX, etc.), its speed and stability have made it an industry standard. Among the various versions, the (often referred to as "EDU" or "Base" depending on firmware) occupies a special place in the hacker and hobbyist community. Released around 2014–2015, the V9 was the last version before Segger introduced significant hardware-based encryption and anti-cloning measures in V10 and V11.
This is the "business end" of the schematic. It handles the signals: TMS/SWDIO: Serial data input/output. TCK/SWCLK: Clock signal. TDI/TDO: Traditional JTAG data lines. RESET: To hardware-reset the target. Many hobbyists use the J-Link V9 schematic to
Finding a schematic is one thing; getting it working is another. Here is what you need to build, program, and debug your own J-Link V9.
Clone schematics frequently omit the expensive protection buffers (like the 74HC24474 cap H cap C 244 ) to keep manufacturing costs rock-bottom.
Using such schematics to build a personal debugger for learning purposes is generally accepted as fair use. However, manufacturing and selling clones that use SEGGER’s proprietary firmware is a violation of the company’s license terms and may infringe on patents or trademarks.