9.2. Enabling the ETM interface

The only input to the ETM interface of the ARM946E-S is an enable signal that determines whether the required ARM9E-S inputs and outputs are driven out from the ARM946E-S.

The ETM enable is controlled by the top-level pin ETMEN. When this input is HIGH, the ETM interface is enabled and the outputs are driven so that an external ETM can begin code tracing.

When the ETMEN input is driven LOW, the ETM interface outputs are held at their last value before the interface is disabled. At reset, all ETM interface outputs are reset LOW.

The ETMEN input is usually driven by the ETM, and driven HIGH when you have programmed the ETM using its TAP controller.

Note

If you do not use an ETM in an embedded ARM946E-S design, you must tie the ETMEN input LOW to save power.

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