Cortex-M Debug Connector

Hi Massimo,

Arduino Due is based on the Cortex-M processor, but why isn't the debugging connector designed for the 10-pin Cortex Debug connector?

CoreSight Technology

It is designed for the ARM Cortex 10-pin SWD connector, as are most Cortex boards:


Ther are to debugging conectors in the Arduino Due schematic.

  1. 10-pin (referred as JTAG) -> JTAG & Serial Wire (SWJ)
  2. 4-pin (referred as DEBUG) -> Specification?

I referred to the 10-pin connector and use the Segger J-Link 9-pin Cortex-M Adapter.
The J-Link 9-pin Cortex-M Adapter allows JTAG, SWD and SWO connections between J-Link and Cortex-M based target hardware systems.

Key pin. Removed from target connector, or physically blocked on debug connector.

and why is this Key pin.(7) not removed from the Arduino Due Board?

All the boards I have use the standard 10 pin connector, as does the CrossConnect JTAG unit that I use.

I don't know where the 9-pin format came from, is it created by Segger? It does not seem to be an ARM standard.

Personally I prefer to use a header with a polarised housing. The key pin does the same job, but I am not going around cutting pins off headers... Seems a bad idea to introduce an incompatible standard, for a marginal improvement.


Segger J-Link 9-pin Cortex-M Adapter has a 10-pin debug connector specified by ARM (Key pin. physically blocked on debug connector.)

Now i have removed the blockade on pin 7 and connect it to the Arduino Due 10-pin connector (referred as JTAG).

But why is there still a the 4-pin (referred as DEBUG) connector?

Hello ctbenery,

That 4 pin header (DEBUG) is a serial wire debug protocol (SWD) connector. It is another simpler protocol that only needs the data and clock lines to talk via serial between the SAM3X8E and the debugger.

In reference to dealing with surface components on the Due, I would recommend to be very careful. It happened to me twice that a capacitors just pop up the board and where hard to find in my workbench floor :). Regards!