2.2.5. SWD and JTAG selection mechanism

SWJ-DP enables one of the following modes to be selected:

When in Dormant mode, the TMS, TDI, and TDO signals can be used for other purposes, enabling alternative debug protocols to be used by other devices connected to the same pins.

The switcher defaults to JTAG operation on power-on reset, therefore the JTAG protocol can be used from reset without sending a selection sequence.

The SWJ-DP contains a mode status output, JTAGNSW, that is HIGH when the SWJ-DP is in JTAG mode and LOW when in SWD or Dormant mode. This signal can be used to:

Another status output, JTAGTOP, indicates the state of the JTAG-DP TAP controller. These states are:

This signal can be used with JTAGNSW to control multiplexers so that, for example, TDO and TDI can be reused as General Purpose Input/Output (GPIO) signals when the device is not in JTAG mode, or during cycles when these signals are not in use by the JTAG-DP TAP controller.

See the ARM Debug Interface v5 Architecture Specification and the ARM Debug Interface v5.1 Architecture Supplement for information on the SWJ-DP switching sequences.

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