Under the control of the ARM debug tools, the ETM7 PWRDOWN output is used to enable and disable the ETM. When PWRDOWN is HIGH, this indicates that the ETM is not currently enabled, so you can stop the CLK input and hold the other ETM signals stable. This enables you to reduce power consumption when you are not performing tracing.

When a TAP reset (nTRST) occurs, PWRDOWN is forced HIGH until the ETM7 control register has been programmed (see the Embedded Trace Macrocell Specification for details of this register).

PWRDOWN is automatically cleared at the start of a debug session.

On the ARM720T processor, the ETM interface pins are gated by the ETMEN input. This means that if the ETMEN input is LOW, all the output pins of the ETM interface remain stable. You can control this ETMEN input by connecting it with either of the following: