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J-Link OB

J-Link OB is an on-board debug probe.
It turns an evaluation board into a complete evaluation kit! 
Added features include debug support and download into Flash memory.
J-Link OB is a cost-effective way to allow customers to fully use, test, and debug the target device right out of the box.

  • Same features as J-Link BASE
  • Fully compatible with J-Link BASE
  • Compatible with most IDEs
  • JTAG, SWD + SWO supported
  • "Drag-And-Drop" interface for intuitive programming of the target device (optional)
  • Virtual COM Port (optional)
  • Very small form factor
  • Allows use of external debug probes



What is the J-Link OB?

The J-Link OB (for On-Board) is essentially a microcontroller-based, single-chip, J-Link that goes right on the evaluation board. It is compatible with, and has the same features as, J-Link BASE with reduced, but still great, performance.

The microcontroller that is used as a J-Link OB (on the left side of the evaluation board in the diagram below) has a USB-interface on its left side (facing the host) and a JTAG/SWD + SWO interface on its right side (facing the target device).


Connecting the PC and the target CPU
using a J-Link OB.


Connecting the PC and the target CPU
using a regular J-Link.

All features of J-Link BASE can be used, including download into Flash memory.

Why use a J-Link OB?

J-Link OB turns an evaluation board into a complete evaluation kit!
It adds features such as debug support and download into Flash memory, without adding significant extra cost.
Customers can fully use, test, and debug the target device (typically a microcontroller) right out of the box.
J-Link OB is compatible with most IDEs including Eclipse, GDB-based IDEs, and SEGGER Embedded Studio. For a complete list, please refer to the Supported IDEs page.

Who uses a J-Link OB?

J-Link OB is used on various evaluation boards, by several evaluation board manufacturers, for numerous target devices.

Additional options

Drag & Drop programming option

Intuitive Programming of the Target Device

Drag-And-Drop is an optional J-Link OB intuitive programming feature. It allows programming of your target MCU in a very simple way.

J-Link OB with Drag-And-Drop capability appears both as a debug probe and as a flash drive on the user's computer.
The high performance and functionality of flash download using a debugger and a J-Link still exists and is as straightforward as ever.
Drag and drop just makes it faster and even easier!
With the flash drive option it is now as simple as dragging and dropping a file (a Motorola S-record, an Intel Hex, or a plain binary) onto the J-Link drive. There is no need to install application software. Anyone that can drag and drop a file to a USB memory stick can now program the target on an evaluation board.

This J-Link Drive enables manufacturers, and third-party software developers, to deploy ready-to-go demonstration applications to customers who can then quickly evaluate the capability of the board, software, and device - all without installing software or drivers. All major operating systems (Windows, macOS, Linux) are supported.

Developed by SEGGER's Embedded Experts Team, J-Link OB offers a compelling opportunity for board manufacturers to provide a highly polished way to deliver integrated solutions to customers, and enhance the experience over time by adding new applications and features that just "drop into place".

Once customers are ready to do more than download fixed demonstration applications, they can unleash the full potential of the target board using the J-Link OB as a debug probe backed by unparalleled, industry-wide support.

This feature uses SEGGER's Virtual MSD technology.

SEGGER - Video Thumbnail Drag and Drop Programming with J-Link OB

Drag & Drop Programming with J-Link OB

Drag-And-Drop Flash Programming in Action

The image below demonstrates how easily the microcontroller on the SEGGER emPower (V2 Rev. D or later) can be programmed via the "Drag-And-Drop" option. 

  1. Connect the J-Link OB to a Windows, Mac or Linux machine via USB and open the file explorer of your choice.
    J-Link will be shown as a flash drive.
  1. Drag and drop one of the demo .hex files (download here) to the J-Link drive. Programming will start as soon as you drop the file.
SEGGER emPower Board
  1. Relax and watch the demo which starts automatically after a few seconds, once programming is complete!

Please note, that Drag-And-Drop is available upon request only. 
If you are interested or need more information, please do not hesitate to contact us at

    Example implementations that support Drag-And-Drop flash programming

    The following boards are already using J-Link OB implementations that support Drag-And-Drop flash programming: 

    Virtual COM Port (VCOM) option

    Virtual COM port (VCOM) is a technology used to replace the traditional COM ports on modern PCs and laptops. From the host’s perspective, there is no difference between a physical (“real”) COM port and a virtual one.
    Virtual COM port enables the J-Link OB to communicate with the host via a USB UART. Any terminal program can be used and this communication channel can also be used for other purposes.
    For some J-Link OBs even multiple VCOMs are available.
    VCOMs can be used in parallel with the J-Link functionality (so while debugging) or even when the J-Link is not in use (when no debug session is active).

    Debug Out option

    J-Link OB is designed to debug the target device.
    Using it to debug a device that is on another board, or to build debug probes (stand-alone J-Links), is not permitted under the standard license.
    However, there is a debug out option, available for an additional charge, which allows using the J-Link OB to program and debug custom hardware.

    The PLUS option

    A standard J-Link OB comes with the same options as J-Link BASE.
    It does not allow the usage of unlimited breakpoints in flash memory, or the use of software packages such Ozone and J-Flash.
    With the PLUS option, all of these software packages are also available to the end user of the J-Link OB.

    Model overview / Supported cores

    J-Link OB is essentially a microcontroller with a USB device interface running J-Link firmware. Below is a list of currently available options for J-Link-OB, along with the supported cores and interfaces.

    Please note that not every J-Link-OB supports every core and every interface/feature. Other microcontrollers can be supported upon request. If you are looking for a combination that is not yet supported, please get in touch with us.

    J-Link OB modelOB DeviceSupported target coresJTAGSWDVCOM
    Drag & Drop
    SWO speedInterface speedDownload performance
    J-Link-OB-K22-Cortex-MNXP MK22FN128VLH10 LQFP64 package No external crystal required Cortex-M4 @ 96MHz, 128 KB flashCortex-M





    4 MHz4 MHz200 KB/s





    J-Link-OB-STM32F072-Cortex-M-128KBST STM32F072CB UFQFPN48 package No external crystal required Cortex-M0+ @48 MHz, 128 KB flashCortex-M





    250 kHz2 MHz100 KB/s
    J-Link-OB-STM32F072-Cortex-M-64KBST STM32F072C8
    UFQFPN48 package
    No external crystal required
    Cortex-M0+ @48 MHz, 64 KB flash





    250 kHz2 MHz100 KB/s





    J-Link-OB-STM32F103-Cortex-MST STM32F103TB
    VFQFPN36 package
    Cortex-M3 @72 MHz, 128 KB flash





    4500 kHz2.25 MHz150 KB/s





    J-Link-OB-SAM3U128Atmel ATSAM3U2C
    LQFP100 package
    Hi-Speed USB
    Cortex-M3 @96 MHz, 128 KB flash





    12000 kHz3.2 MHz225 KB/s
    Available, but not recommended for new designs
    J-Link-OB-SAM7S64Atmel SAM7S64
    LQFP64 package
    ARM7 @48 MHz, 64 KB flash





    6000 kHz12 MHz700 KB/s


    Not supported


    1 Optional. Needs to be specified when ordering

    Starter kits

    J-Link OB Starter kits are available which allow eval board manufacturers to test the suitability of J-Link OBs on their specific eval board.
    The following J-Link OB Starter kits are available:

    StarterKit J-Link-OB-K22

    The StarterKit J-Link-OB-K22 contains the following components:

    • J-Link OB programming utility for testing and production purposes
    • Documentation which includes schematic for J-Link-OB-K22
    • Support

    J-Link OB K22 Eval reference board

    StarterKit J-Link-OB-STM32F072

    The StarterKit J-Link-OB-STM32F072 contains the following components:

    • J-Link OB programming utility for testing and production purposes
    • Documentation which includes schematic for J-Link-OB-STM32F072
    • Support

    J-Link OB STM32F072 Eval reference board

    StarterKit J-Link-OB-SAM3U

    The StarterKit J-Link-OB-SAM3U contains the following components:

    • J-Link OB programming utility for testing and production purposes
    • Documentation which includes schematic for J-Link-OB-SAM3U
    • Support

    J-Link OB SAM3U Eval reference board

    StarterKit J-Link-OB-STM32F103

    The StarterKit J-Link-OB-STM32F103 contains the following components:

    • J-Link OB programming utility for testing and production purposes
    • Documentation which includes schematic for J-Link-OB-STM32F103
    • Support

    J-Link OB STM32F103 Eval reference board

    After evaluation of the J-Link OB, a production license needs to be purchased with information on the selected J-Link OB device. The following conditions apply for the usage of the J-Link OB technology:

    • SEGGER Logo needs to be printed on the PCB of each eval board containing the J-Link technology
    • Eval board does not provide debug out option
    • 2 eval board samples containing J-Link OB technology will be provided to SEGGER FOC

    Licensing options

    Who Can License J-Link OB?

    Originally J-Link OB was intended to be licensed by evaluation board manufacturers and silicon vendors at very reasonable prices.

    Later, requests came from companies for in-house use, and for use in developing products whereby the J-Link OB stays with the product after development. 

    Evaluation board manufacturers

    Under the license for evaluation board manufacturers, the J-Link OB is provided solely as part of an evaluation board. It is not sold separately and may only be used to debug the device on the evaluation board it comes with. 

    Support is provided via the evaluation board manufacturer and via SEGGER Forum. J-Link OB may not be used for production purposes.

    Commercial use

    J-Link OB can be licensed to be designed in a product or a software development board (for setting up an automated test environment etc.). For this type of license pricing is available upon request.


    A Buy-out license is available upon request.


    For publicly available evaluation boards with a single Cortex M Processor, the price of a J-Link OB license without add-ons is 10 cents per board for quantities of 10k or more.

    Different pricing applies if J-Link OB is used in other projects such as in-house development boards, or in final products, or use of a different target processor, or if you are interested in adding options, such as Drag and Drop, Debug out, and Virtual COM Port.

    Buy-outs (one-time cost, with no per board cost, no royalties) are also available.

    Required quotation information

    For SEGGER to prepare a quotation we need answers to the questions below:

    1. Usage: Do you want to place the J-Link OB on a publicly available evaluation-board? If not, what is the intended use?
    2. Model: What J-Link OB model do you need licenses for?
    3. Target device: What is the name and manufacturer of the target device that is being debugged with this J-Link OB?
    4. VCOM: Do you need VCOM functionality in this J-Link OB? If yes, would you like to enable hardware flow control functionality in this J-Link OB?
    5. Drag & Drop programming: Do you need drag & drop support in this J-Link OB?
    6. Debug out: Would you like to have a connector or other option that allows/enables debugging of external devices?


    How big can the virtual drive be?

    A: Pretty much any size. Typically, the size of the virtual J-Link drive should be at least 2.5 times as large as the size of the flash memory, typically rounded to a power of 2. So for a 256KB device, 1MB or more is a good choice. For a 4MByte flash device, the capacity should be 16MB.

    Who does the configuration for the target device?

    A: All of this is done by SEGGER. The customer receives a production utility that programs the J-Link OB correctly, with the capability to program the specified target device.

    The device we target has large flash sectors of up to 128KB per sector. Is this a problem?

    A: No. J-Link OB can cope with this.

    How fast is the flash programming?

    A: Quite fast. Basically as fast as the target device allows it. Total programming time is just slightly more than the time it takes to erase and program the device with very little overhead. On a Nordic Semiconductor NSxxx it takes about 3 seconds to erase and program the entire 256KB flash.

    How can this be so fast?

    A: Simple: J-Link OB uses SEGGER's real time OS embOS. Multiple tasks run in parallel, performing multiple operations simultaneously: Downloading the program via USB to the J-Link OB, as well as downloading from the J-Link OB into the RAM of the target device as well as "copying" the RAM content of the target device into flash (the actual flash programming). All run largely in parallel, so that the speed is determined by the slowest of the 3 operations, typically the actual flash programming inside of the target device.

    What are the minimum hardware requirements for the J-Link OB?

    A: Pretty much the same as for J-Link: 64KB Flash memory, 16KB RAM. The only additional requirement is that the MCU used as J-Link OB needs to have a sufficient number of USB Endpoints to accommodate the MSD: 1 for control, 2 bulk for J-Link, 2 bulk for MSD. 

    Can J-Link work with any kind of Hex or Mot file? Even if only a part of the flash is programmed or the address range is non-consecutive?

    A: Yes