C.2.1. Combined pin names

Table C.1 shows a summary of the pin names.

Table C.1. Summary of pin names

Pin numberCombined pin namePin numberCombined pin name
1VTref11Gnd/TgtPwr+Cap
2TMS/SWDIO12TraceClk/RTCK
3GND13Gnd/TgtPwr+Cap
4TCK/SWCLK14TraceD0/SWO
5GND15GND
6TDO/SWO/EXTa/TraceCtl16TraceD1/nTRST
7Key17GND
8TDI/EXTb/TraceCtl18TraceD2/TrigIn
9GNDDetect19GND
10TraceCtl/nRESET20TraceD3/TrigOut

See Table C.4 for a generic description of the pins.

The following sections describe the use of pins 6, 8, 11, and 13:

EXTa and EXTb pins

Some pins on the connector have functions that are only used for certain connection layouts. Where a pin is not required for a particular debug communication protocol, it can be reused for a user-defined target function. These pins are labeled EXTa and EXTb in the tables in this appendix. You must select any alternate functions carefully, and also consider the effects of connecting debug equipment capable of communicating using multiple protocols.

GND/TgtPwr+Cap pins

There are two usage options for these pins:

Target boards

Standard target boards can connect these two pins directly to signal ground, GND.

Some special target boards, typically those for evaluation or demonstration purposes, can use these pins to supply power to the target board. In this case, the target board must include capacitors between each of the pins and signal ground. The capacitors must be situated extremely close to the connector so that they maintain an effective AC ground, that is, high frequency signal return path. Typical values for the capacitors are 10nF.

Debug equipment

Debug communication equipment designed to work with special valuation or demonstration target boards provides operating current, typically up to 100mA, at a target-specific supply voltage, for example, 3.3V, 5V, or 9V. ARM recommends that the debug equipment includes some protection if you connect it to standard target boards that have connected these pins directly to GND, for example, a current limiting circuit. This debug equipment must include capacitors between each of these power pins and signal ground. The capacitors must be situated extremely close to the connector so that they maintain an effective AC ground, that is, high frequency signal return path. Typical values for the capacitors are 10nF.

Standard debug communication equipment can connect these pins directly to GND. It is also possible for these pins to have only a high frequency signal return path to ground, using 10nF capacitors. This option is also compatible in the unlikely case where a target board has a connection between the debug connector TgtPwr pins, but is powered from another source.

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