C.2.3. 20-way connector pinouts including trace

20-way connectors include support for a narrow trace port, up to four data bits, operating at moderate speed, up to 100 MSamples/sec. They are described in:

Table C.3 shows the 20-way header for targets using SWD or JTAG for debug communication, and includes an optional SWO signal for conveying application/instrumentation trace. Alternatively, a target trace port operating in CoreSight normal or bypass modes might convey the TraceCtl signal on pin 6.

Both pin 6 and pin 8 in the SWD layout are shown with alternative extra signals, EXTa and EXTb. This enables flexibility to communicate other signals on these pins. For example, future target systems and trace equipment might convey two more trace data signals on these pins.

Table C.3. 20-way connector for future SWD or JTAG systems

Pin name for SWDPin numberPin name for JTAGPin number
20-wayMictor20-wayMictor
VTref112VTref112
SWDIO217TMS217
GND3-GND3-
SWCLK415TCK415
GND5-GND5-
SWO/EXTa/TraceCtl611TDO611
Key7-Key7-
NC/EXTb8(19)TDI819
GNDDetect9-GNDDetect9-
nRESET109nRESET109
Gnd/TgtPwr+Cap11-Gnd/TgtPwr+Cap11-
TraceClk126TraceClk126
Gnd/TgtPwr+Cap13-Gnd/TgtPwr+Cap13-
TraceD01438TraceD01438
GND15-GND15-
TraceD11628TraceD11628
GND17-GND17-
TraceD21826TraceD21826
GND19-GND19-
TraceD32024TraceD32024

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. This layout s the recommended debug connection for a processor built with support for instruction trace, that is, including an ETM.

Note

  • A target board can use this layout 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.3. 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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