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J-Trace Isolator

The J-Trace Isolator can be connected between a J-Trace Pro V2 or later and any ARM-board that uses the standard 19-pin Cortex-M connector to provide electrical isolation while keeping high speed trace capabilities.

  • ETM trace pins fully supported up to 75 MHz Traceclock
  • 1 kV DC isolation
  • 1.2 V - 5 V target operation supported
  • Powered from emulator, only few microamps (< 25 µA) drawn from target
  • JTAG standard 19-pin connection supporting TDI, TMS, TCK, TDO, RESET and SWD/SWO signals
  • SWD frequency: Up to 4 MHz
  • JTAG frequency: Up to 50 MHz
  • 3 LEDs to indicate emulator power, target power and target RESET



Typical Fields of Application

The J-Trace Isolator can be connected between a J-Trace Pro V2 or later and any ARM-board that uses the standard 19-pin Cortex-M connector to provide electrical isolation while keeping high speed trace capabilities. This is essential when the development tools are not connected to the same ground as the application.

It is also useful to protect the development tools from electrical spikes that often occur in some applications, such as motor control applications. Another typical field of application is development of products with sensors or other analog circuitry, in which case the target hardware is protected from electrical noise originating from the development PC. The J-Trace Isolator is compatible with J-Trace Pro V2 or later.

Trace Specification

The J-Trace Isolator supports Traceclocks up to 75 MHz. For Reference the following Project can be used with the Cortex-M Trace Reference board that is included in each J-Trace Pro package:

Download   TraceIsolator Example for Cortex-M Trace Reference board

Faster Traceclocks are beyond the specification of the digital isolator IC. Nonetheless speeds up to 120 MHz were already achieved in an example setup with this project: (testing at room temperature, with a slight adjustment of sampling delays in J-Trace PRO V2).

More information can be found here:

Power Supply

Other than the J-Link Isolators the J-Trace Isolator does not have to be powered additionally from target side reducing the power consumption footprint of the debug setup to < 25µA.

The emulator side powers the complete Isolator logic through pins 11 and 13.

Minimum Requirements

A J-Trace PRO Cortex/Cortex-M V2 or later is required to supply power to the J-Trace Isolator.

Older models might not support powering the targer side through the debug interface.

An overview with all software and hardware features of all our debug probe models can be found here.


Connectors and Indicators


The J-Trace Isolator uses high speed digital isolators that allow a very low propagation time between input and output. It comes with the following connectors and indicators:

PIN Layout

  • Standard .05" 19-pin Cortex-M male EMULATOR connector which needs to be connected to the emulator cable
  • Standard .05" 19-pin Cortex-M male TARGET connector for connection of the target cable
  • Green LED indicating power on the emulator side
  • Green LED indicating power on the target side
  • Red LED indicating RESET

Block Diagram

The following functional block diagram illustrates the functional connections between the emulator and target.


Target Connector

The following pictures show the target side pinout of the J-Trace Isolator when used with SWD or JTAG respectively:

Pin 1VTrefInput This is the target reference voltage. It is used to check if the target has power, to create the logic-level reference for the input comparators and to control the output logic levels to the target. It is normally fed from Vdd of the target board and must not have a series resistor.
Pin 2SWDIO/ TMSI/O / OutputJTAG mode set input of target CPU. This pin should be pulled up on the target. Typically connected to TMS of the target CPU.
Pin 4SWCLK/TCKOutputJTAG clock signal to target CPU. It is recommended that this pin is pulled to a defined state of the target board. Typically connected to TCK of the target CPU.
Pin 6SWO / TDO Input JTAG data output from target CPU. Typically connected to TDO of the target CPU.
---------This pin (normally pin 7) is not existent on the 19-pin JTAG/SWD and Trace connector.
Pin 8TDI OutputJTAG data input of target CPU.- It is recommended that this pin is pulled to a defined state on the target board. Typically connected to TDI of the target CPU.
Pin 9NCNCNot connected inside J-Link. Leave open on target hardware.
Pin 10nRESETI/OTarget CPU reset signal. Typically connected to the RESET pin of the target CPU, which is typically called "nRST", "nRESET" or "RESET".
Pin 12TRACECLKInputInput trace clock. Trace clock = 1/2 CPU clock for Cortex-M devices.
Pin 14 TRACEDATA[0]InputInput Trace data pin 0.
Pin 16 TRACEDATA[1] InputInput Trace data pin 1.
Pin 18 TRACEDATA[2] InputInput Trace data pin 2.
Pin 20 TRACEDATA[3] InputInput Trace data pin 3.

Pins 3, 5, 15, 17, 19 are GND pins connected to GND.


Using the J-Trace Isolator with J-Trace PRO

In order to use the Isolator, follow these steps:

  • Connect the Isolator with J-Trace Pro
  • Power J-Trace Pro
  • Make sure the green LED on the emulator side is lit. If it is not, please follow the instructions below
  • Connect the target to the target side of the Isolator
  • If the target is powered, the green LED on the target side should be lit 

The red LED on the target side is lit when a Target RESET is active (low).

Preparing J-Trace to Supply Power

J-Trace needs to supply 5V power to the emulator side of the adapter on pin 11 and pin 13. In order to do this, you may have to configure J-Trace once as follows:

  • Make sure that SEGGER J-Link software is installed on your machine. It can be downloaded from here:
  • Start J-Link Commander, which can be found under “Start -> Programs -> SEGGER ->”
  • Enter the following command: power on perm
  • Plug in the adapter: The LED on the emulator side should now be lit.

The red LED on the target side is lit when a Target RESET is active (low).

Using the J-Trace Isolator with another ARM Emulator

The Isolator has been designed for J-Trace Pro V2 or later, but can also be used with other ARM emulators with the same pin-out. In this case, you should make sure that 5V are supplied to pin 19 of the emulator connector and that your emulator is not damaged when applying 5V to this pin. Do this at your own risk!


This isolator provides basic isolation only. Do not use with hazardous voltages without further protection measures to avoid risk of electrical shock and fire.

SEGGER isolators provide a basic isolation to withstand high voltages as mentioned in the resp. technical data section. To preserve integrity of human beings when dealing with potential hazardous voltages it is mandatory to have a second protection measure in place in case the first insulation barrier fails. This is called double or reinforced isolation. How this double isolation can be achieved depends on the use case or application setup. Also check your the local safety related directives valid for your country to make sure all requirements are met.

Package Content


J-Trace Isolator


.05" 20-pin ribbon cable