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Hot-plug the debug cable

At times, you might want to connect or disconnect the debug cable between the DSTREAM-PT system and the target hardware, without powering off the target. This process is known as hot-plugging.

Arm recommends you avoid hot-plugging the debug cable, however, you can hot-plug without affecting operation of the target, if:

  • The DSTREAM-PT system is powered by its original power supply (which has an earthed-output).
  • The target hardware is earthed, either through its power supply, or a separate earth connection.


If the DSTREAM-PT system or the target hardware are not properly earthed, potential differences can occur between them. During connection, potential differences can cause unwanted pulses in the debug interface. Pulses in the debug interface can cause unwanted resets to occur.

Hot-plugging: connecting

To connect a DSTREAM-PT system to a target without affecting its current state, you must:

  1. Power up the DSTREAM-PT system. Allow the DSTREAM-ST and Parallel Trace probe to boot up.
  2. Connect the debug cable to the target.


    When connecting the debug cable to the target system, to guard against ground-loop noise, ensure that one of the GND pins of the debug connector makes contact first. This contact ensures that the current target state is not affected. For pin details, see Target interface connections in the Arm® DSTREAM-PT System and Interface Design Reference Guide.

Hot-plugging: disconnecting

When unplugging the debug connector, you must be aware that:

  • If you are using a Return Test Clock (RTCK) system, make sure that no communication is taking place between the system and the DSTREAM-PT system. Otherwise, if the DSTREAM-PT system is waiting for a return clock, it might lock up.
  • If you are not using an RTCK system, the debug software can handle this situation. However, you must perform a Test Access Port (TAP) reset using the debugger when you next connect the DSTREAM-PT system to a target. For more information on TAP resets, see Reset signals.
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