2.2.3. JTAG and SWD interface

The external JTAG interface has four mandatory pins, TCK, TMS, TDI, and TDO, and an optional reset, nTRST. JTAG-DP and SW-DP also require a separate power-on reset, nPOTRST.

The external SWD interface requires two pins:

The block level interface has two pins for data plus an output enable that must be used to drive a bidirectional pad for the external interface, and clock and reset signals. To enable sharing of the connector for either JTAG or SWD, connections must be made external to the SWJ-DP block, as shown in Figure 2.6. In particular, TMS must be a bidirectional pin to support the bidirectional SWDIO pin in SWD mode. When SWD mode is used, the TDO pin is expected to be re-used for Serial Wire Output (SWO). You can use the TDI pin as an alternative input function.


If you require SWO functionality in JTAG mode, you must have a dedicated pin for TRACESWO.

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