With the VCOM feature, a single cable can provide both programming/debugging and a serial console connection – a huge convenience for development.
A detailed analysis of the JLink V9 schematic reveals a well-designed and optimized layout. The schematic can be divided into several sections:
The open-source world offers several variations of the J-Link V9 schematic. You'll generally encounter two main types:
Disclaimer: This article is for educational purposes only. The author does not provide or distribute schematics for Segger products. All trademarks are property of their respective owners. jlink v9 schematic
The physical interface defined by the schematic follows the classic ARM standard JTAG pinout layout. Pin Number Signal Name Description Target Reference Voltage (Used to power level shifters) 2 Optional 5V power supply to target board 3 JTAG Tap Reset (Not used in SWD mode)
: A double-sided PCB that includes ESD protection, optional USB isolation (using ADUM3160), and switchable 3.3V output. This design has been fabricated and tested by numerous community members.
The actual achievable speed depends heavily on the target’s debug interface and the quality of the signal connections (cable length, grounding). With the VCOM feature, a single cable can
Some clones also report using the STM32F205VG, which offers 1MB of Flash—more than enough for the most feature-complete firmwares. The general consensus across the community is that the STM32F205 series represents the “sweet spot” for J-Link V9 designs, balancing performance, memory capacity, and cost.
A correctly designed V9 can achieve:
A dedicated circuit for the pin (Pin 15) to allow the probe to force a hardware reset on the target. Isolation You'll generally encounter two main types: Disclaimer: This
While SEGGER never released official schematics, the community has produced several high-quality open-source V9 designs. The most referenced source appears to be the work of a user known as , whose original schematic—later modified and improved by others—has become the de facto reference for DIY J-Link V9 projects.
The J-Link v9 hardware is a significant upgrade over the older v8, primarily moving to a faster and more stable 32-bit RISC CPU .