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J-Link OB

J-Link OB is a single chip microcontroller "on-board" of YOUR eval board. The microcontroller has a USB-interface on one side and a JTAG/SWD + SWO etc. interface on the device side. It allows debugging the target device on the board it comes with, without the need for an additional debug probe.

J-Link OB is used on various eval boards by several eval board manufacturers for various target CPUs.


  • Fully compatible to and same features as regular J-Link
  • Inexpensive solution for complete evaluation kits with debug functionality
  • JTAG, SWD + SWO supported
  • Virtual COM Port (STM32F072, SAM3U)
  • Optional disable allows use of other external debug probes
  • Compatible with most IDEs
  • Very small form factor (J-Link OB on eval board example)
  • "Drag-And-Drop" interface for intuitive programming of the target device


PDF J-Link documentation download 

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Why J-Link OB?

Having a J-Link right on the eval board allows customers to fully use and test the target CPU, providing full debug capabilities. At the same time, the eval board can remain small and inexpensive (J-Link OB on eval board example). All features of the regular J-Link can be used, including download into Flash memory.


J-Link OB is provided as part of an evaluation board. It is not sold separately. It may only be used to debug the device on the evaluation board it came with.
Support is given via the eval board manufacturer and via SEGGER forum. J-Link OB may not be used for production purposes.

Basic concept

The pictures below show the connection between a PC and the target CPU using the regular J-Link and a J-Link OB.

Connection via regular J-Link:
The PC is connected to J-Link via USB and J-Link connects to the eval board via JTAG debug connector.

Connection via J-Link OB:
The PC is connected to the eval board via USB connector of the J-Link OB. No separate debug connector required!

J-Link OB Reference Board

The picture shows an example of a basic evaluation board for an STM32F205RCT6 target MCU with a J-Link OB based on STM32F072C8.

J-Link OB measured

Click to enlarge
The J-Link OB (not greyed out area in the picture to the left) only takes 3.8 cm² board space which can be further reduced depending on selected components and used PCB technology.

The board space is split to

  • 2.1 cm² J-Link OB MCU circuitry (STM32F072C8 in a 7x7 mm UFQFPN48 package)
  • 1.5 cm² Mini USB connector (will be even less with a Micro USB)
  • 0.2 cm² Pads for needle programming connector

This low cost J-Link OB eval board is manufactured in standard 2 layer PCB technology. It is available as reference board for purchase.

J-Link OB model overview

J-Link OB is not much more than a microcontroller with 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 model OB Device Supported target cores Supported
Target Interfaces
Drag & Drop
J-Link-OB-STM32F072-Cortex-M-128KB ST STM32F072CB
UFQFPN48 package
No external crystal required
Cortex-M0+ @48 MHz, 128 KB flash
J-Link-OB-STM32F072-Cortex-M-64KB ST STM32F072C8
UFQFPN48 package, 1$2
No external crystal required
Cortex-M0+ @48 MHz, 64 KB flash
J-Link-OB-STM32F072-Cortex-A-64KB ST STM32F072C8
UFQFPN48 package, 1$2
No external crystal required
Cortex-M0+ @48 MHz, 64 KB flash
J-Link-OB-STM32F103-Cortex-M ST STM32F103TB
VFQFPN36 package
Cortex-M3 @72 MHz, 128 KB flash
J-Link-OB-STM32F103-Cortex-A ST STM32F103TB
VFQFPN36 package
Cortex-M3 @72 MHz, 128 KB flash
J-Link-OB-SAM3U128 Microchip ATSAM3U2C
LQFP100 package
Hi-Speed USB
Cortex-M3 @96 MHz, 128 KB flash
Available, but not recommended for new designs
J-Link-OB-SAM7S64 Atmel SAM7S64
LQFP64 package
ARM7 @48 MHz, 64 KB flash

2 Approximate silicon costs, based on 10k quantities

1 Optional. Needs to be specified when ordering

Drag-And-Drop option: Intuitive programming of the target device

Drag-And-Drop is a an optional J-Link OB intuitive programming feature. It allows programming 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 - similar to a USB stick. The J-Link's high performance and functionality for programming and debugging remain unchanged! The additional flash drive capability simplifies programming the target to dragging a Motorola S-record, Intel Hex, or plain binary file onto the J-Link Drive using the desktop.

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 complex development software.
All major operating systems (Windows, MAC OS, Linux) are supported and existing OS drivers already support J-Link Drive.

When customers outgrow the convenience of J-Link Drive and 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.

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".

FAQs on J-Link OB Drag-And-Drop flash programming


How big can the virtual drive be?


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?


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 as problem?


No. J-Link OB can cope with this.


How fast is the flash programming?


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?


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?


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?



J-Link OB Drag-And-Drop flash programming in use

The image below demonstrates how easy an MCU can be programmed via "Drag-And-Drop" option.

1) Open a file explorer of your choice. J-Link will be shown as a flash drive.
2) Drag and drop a Bin, Hex or Mot file to the J-Link drive. Programming will start as soon as you drop the file.

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:

J-Link OB Starter Kit

A J-Link OB Starter Kit is available which allows eval board manufacturers to test the suitability of J-Link OBs on their specific eval board.

The Starter Kit contains the following components:

  • 10 Test licenses
  • J-Link BASE
  • J-Link Needle Adapter
  • J-Link OB Reference Board
  • J-Link OB programming utility for testing and production purposes
  • Documentation which includes schematic for the selected OB. For available devices please check "Which devices can be used as J-Link OB".
  • Support

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


Who can license J-Link OB?

J-Link OB is intended to be licensed for evaluation board manufacturers and silicon vendors. We offer a very reasonable pricing. Do not hesitate to contact us at for more information.