C.2.2. 10-way connector pinouts

There are two types of the pinout for a 10-pin connector, one supporting communication using SWD, and one using JTAG, and these are arranged to facilitate dynamic switching between the protocols.

SWD is the preferred protocol for debugging because it provides more data bandwidth over fewer pins, therefore freeing some for use by application functions. JTAG can be used where the target is communicating with a tool chain that does not support SWD, or with test tools performing board-level boundary scan testing, where it might be acceptable to sacrifice the functional pins multiplexed with JTAG.

Table C.2 shows the 10-way header for targets using SWD or JTAG for debug communication, and includes an optional Serial Wire Output (SWO) signal for conveying application and instrumentation trace.

Table C.2. 10-way connector for SWD or JTAG systems

Pin name for SWDPin numberPin name for JTAGPin number
10-wayMictor10-wayMictor
VTref112VTref112
SWDIO217TMS217
GND3-GND3-
SWCLK415TCK415
GND5-GND5-
SWO611TDO611
Key7-Key7-
NC/EXTb819TDI819
GNDDetect9-GNDDetect9-
nRESET109nRESET109

The SWD layout is typically used in a CoreSight system that uses a SWJ-DP operating in SWD mode.

The JTAG layout is typically used in a CoreSight system including a JTAG-DP, or one with a SWJ-DP operating JTAG mode, possibly because it is cascaded with other JTAG TAPs.

Note

  • A target board can use this connector for performing board-level boundary scan but then switch its SWJ-DP into SWD mode for debugging according to the layout shown in Table C.2. This frees up pins 6 and 8 for either application functions or SWO.

  • You do not have to choose the switching mode at the time of chip or board development. The connector can be switched and the target board operated in either SWD or JTAG mode.

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