16.7.3 Serial Wire Debug Port (SW-DP) Pins
The SW-DP pins SWCLK and SWDIO are commonly provided on a standard 20-pin JTAG connector defined by ARM. For more details on voltage reference and reset state, refer to the "Signal Description" chapter.
At startup, SW-DP pins are configured in SW-DP mode to allow connection with debugging probe.
SW-DP pins can be used as standard I/Os to provide users more general input/output pins when the debug port is not needed in the end application. Mode selection between SW-DP mode (System I/O mode) and general I/O mode is performed through the AHB Matrix Chip Configuration registers (CCFG_SYSIO). Configuration of the pad for pullup, triggers, debouncing and glitch filters is possible regardless of the mode.
The JTAGSEL pin is used to select the JTAG boundary scan when asserted at a high level. It integrates a permanent pulldown resistor of about 15 kΩ to GND, so that it can be left unconnected for normal operations.
The JTAG debug ports TDI, TDO, TMS and TCK are inactive. They are provided for Boundary Scan Manufacturing Test purposes only. By default the SW-DP is active; TDO/TRACESWO can be used for trace.
| Pin Name | JTAG Boundary Scan | Serial Wire Debug Port |
|---|---|---|
| TMS/SWDIO | TMS | SWDIO |
| TCK/SWCLK | TCK | SWCLK |
| TDI | TDI | – |
| TDO/TRACESWO | TDO | TRACESWO (optional: trace) |
SW-DP is selected when JTAGSEL is low. It is not possible to switch directly between SW-DP and JTAG boundary scan operations. A chip reset must be performed after JTAGSEL is changed.