Electrical – My first MCU PCB and a new JTAG Cortex + ETM connector

armcortex-m4jtagpcb

I am trying to build my own PCB with a Cortex-M4 microcontroller LPC4088. I decided that JTAG still is the easiest option for programming it. But ARM has implemented a new 0.05'' pitch SAMTEC micro connector.

I own a SEGGER J-link EDU which implements an older 0.1'' pitch connector and in order to use new connector I bought this adapter from SEGGER.

I soon found out that older ARM connectors implemented different pinning than the one used in my new adapter.

The old one (named ARM 20-pin I think):

enter image description here

The new one (named ARM 19-pin Cortex debug + ETM):

What does "—" stand for? Is "N_RESET" pin same as "TRST" in older scheme? Can I leave pins 11 and 13 unconnected?

enter image description here

So I am trying to figure how to plan the connector on my PCB in order to work with my new adapter. So this is what I managed to do so far:

enter image description here

But as you see there are some pins which I don't know what to do with them… So If anyone could please tell me where to connect them I would be really happy. Pin details for LPC4088 can be found on page 10 of the first link that I posted.

Best Answer

As brhans said, you can just use a standard JTAG. What I did on a recent design, I placed both a trace connector (for debugging) and a simple SWD connector (for production programming).

If you do want to put an Trace connector on your board, here are your answers:

  • Pin 7 is not fitted and acts as a key to prevent the connector from being plugged in backwards. The hole is plugged on some receptacles.
  • N_RESET is MCU reset.
  • Pins 11 and 13 are power supply pins from the programmer to the target hardware. You can leave them floating if unused.

Also, have a look at the JLink manual, page 400.