9.2. Enabling the ETM interface

The top-level pin ETMEN enables the ETM interface. When this input is HIGH, the ETM interface drives the outputs so that an external ETM can begin code tracing.

When the ETMEN input is LOW, the ETM interface outputs remain at their last value before the interface was disabled.

The ETM usually drives the ETMEN input HIGH after the debugger programs the ETM using its TAP controller.

ARM recommends that you connect the ETMEN input to the PWRDOWN output of the ETM9 through an inverter as Figure 9.1 shows.

Note

If your design does not include an ETM, tie the ETMEN input LOW to save power.

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