Jlink V9 Schematic Jun 2026

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 heart of most open-source J-Link V9 designs is an STM32 microcontroller, most commonly the or STM32F205RC . This choice is not accidental: jlink v9 schematic

VTref (Target Voltage Reference) - Senses target voltage. Pin 7: SWDIO/TMS. Pin 9: SWCLK/TCK. Pin 15: RESET. Pin 19: power for the target (optional). 3.4. Level Shifter/Buffer Block The 20-pin standard JTAG/SWD connector brings the (Target

Power enters via the USB VBUS pin. It passes through a protection network (including ESD diodes and a PTC resettable fuse) to prevent overcurrent from damaging the PC. It has a "VccA" side connected to the J-Link's internal 3

: External crystal oscillators provide the necessary clock signals for the STM32 microcontroller to maintain high-speed communication (up to 20MHz for JTAG). Key Schematic Components