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The J-Link V9 includes a dual-LED indicator (or two separate LEDs) to show operational status:
Some clones require specific firmware to avoid being bricked by official Segger software updates. Common Failure Points:
These LEDs are driven directly by the main MCU GPIO pins through current-limiting resistors (usually 6. Troubleshooting Common Issues in J-Link V9 Schematics
If you intend to integrate a J-Link V9 circuit directly onto a custom development board for "on-board" debugging (OB), keep these best practices in mind during PCB layout:
Based on typical V9.5 schematics, the circuit is built around these primary components: A. The Microcontroller (MCU) jlink v9 schematic
Many V9 schematics feature a small bridge or short-circuit cap header allowing you to pass 5V or 3.3V back through the probe to power small test boards directly. 🔌 The 20-Pin JTAG/SWD Interface
The SEGGER J-Link V9 is one of the most widely used JTAG/SWD debug probes in the embedded systems industry. For engineers, hardware hackers, and makers, understanding or replicating its schematic is a highly valuable pursuit for custom debugger integration, troubleshooting, or educational purposes.
High-speed, dual-supply translating transceivers like the 74LVC2T45 or 74AVC4T245 are typically deployed.
If you work with ARM microcontrollers, the Segger J-Link is the industry standard. It’s the debug probe that every other probe is compared against. But while Segger is famous for their software—the J-Link SDK, RTT, and their blazing-fast download speeds—the hardware itself is often treated as a "black box." The J-Link V9 includes a dual-LED indicator (or
Looking at the PCB layouts and "leaked" reference schematics:
These ICs (like the 74LVC series) bridge the voltage gap between the SAM3U4E (fixed 3.3V) and your target board (variable voltage). 3. JTAG/SWD Output Stage
: Optional 5V power output to the target board. Performance Comparison J-Link v8 J-Link v9 Main Controller ATMEL AT91SAM7S Main Controller STM32F205 / F207 Max JTAG Speed ~12 MHz Max JTAG Speed Up to 20 MHz Lower Up to 15 MHz Moderate Improved firmware stability
The physical interface on the schematic follows the standard SEGGER 20-pin layout. Below is the exact schematic mapping for the connector: Pin Number Signal Name Description Target Reference Voltage (Used to power level shifters) 2 Optional 5V power supply output to target board 3 JTAG Target Reset (Active Low) 4, 6, 8, 10, 12, 14, 16, 18, 20 Ground Reference 5 JTAG Test Data Input 7 TMS / SWDIO JTAG Test Mode Select / Serial Wire Data Input/Output 9 TCK / SWCLK JTAG Test Clock / Serial Wire Clock 11 Return Test Clock (Used for adaptive clocking) 13 JTAG Test Data Output / Serial Wire Output trace 15 Target System Reset (Active Low) 17 Debug Request (Rarely used in modern ARM cores) 19 Alternative 5V supply pin 5. Status Indicators and Auxiliary Circuitry The Microcontroller (MCU) Many V9 schematics feature a
Professional probes feature array diodes on data lines to stop electrostatic discharge when plugging cables into live circuit boards. Cheap schematics omit these entirely to save space.
To tailor this technical architecture information to your exact project goals, please consider how you would like to proceed.
At the absolute center of any J-Link V9 schematic, you will find the STMicroelectronics STM32F205RCT6 Microcontroller . Why did the designers choose this specific chip?
This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later. J-Link Interface Description - SEGGER
A dedicated circuit for the pin (Pin 15) to allow the probe to force a hardware reset on the target. Isolation
isolation resistor or a cracked solder joint right at Pin 1 of the connector. "USB Device Not Recognized" The computer fails to enumerate the ATSAM3U chip.
