Hot-Plugging The Debug Cable - ARM DSTREAM-ST Getting Started Manual

3.2

Hot-plugging the debug cable

At times, you might want to connect or disconnect a debug cable without powering off the target. You
can do this provided certain conditions exist.
You can connect and disconnect the DSTREAM-ST unit to the target hardware without affecting
operation of the target if:
• The DSTREAM-ST unit is powered by its original, earthed-output power supply.
• The target hardware is earthed either through its power supply or a separate earth connection.
If the DSTREAM-ST unit or the target hardware are not properly earthed, potential differences can occur
between them, causing unwanted pulses in the debug interface during connection. This can cause
unwanted resets to occur.
In a scenario where the DSTREAM-ST unit is not connected to your target, but the target behavior has to
be analyzed without affecting its current state, you must:
• Power up the DSTREAM-ST unit before connecting to the target.
• After the DSTREAM-ST unit is powered up, connect the debug cable to the target.
• As an added precaution to guard against ground-loop noise, it is advisable to ensure that one of the
GND pins of the debug connector makes contact first when connecting the debug cable to the target
system. See ARM DSTREAM-ST Target Interface Connections chapter in the ARM DSTREAM-ST
System and Interface Design Reference Guide for pinout details.
Doing so ensures that the current target state is not affected in any way when you connect DSTREAM-
ST unit to the target.
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-ST unit. Otherwise, if the DSTREAM-ST unit 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 arrange to do a Test Access Port (TAP) reset using the debugger when you next plug the
DSTREAM-ST unit into a target.
ARM 100892_0100_00_en
Note
Copyright © 2017 ARM Limited or its affiliates. All rights reserved.
Non-Confidential
3 Working with ARM DSTREAM-ST
®
3.2 Hot-plugging the debug cable
3-25