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.

  • \$\begingroup\$ If you're designing your own PCB then why don't you just use whatever connector mates to the JTAG programmer you already have? The MCU doesn't know or care what the mechanical hardware looks like .... \$\endgroup\$
    – brhans
    Mar 17, 2016 at 12:35
  • 1
    \$\begingroup\$ TRST (or usually nTRST) is not the same as RST or N_RST. nTRST is the JTAG-reset while RST is usually the processor/uC-reset. \$\endgroup\$
    – og1L
    Mar 17, 2016 at 16:19

1 Answer 1


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.

  • \$\begingroup\$ Thank you for the refference. One more thing. Should I use pullup on reset? \$\endgroup\$
    – 71GA
    Mar 18, 2016 at 10:51
  • 1
    \$\begingroup\$ @71GA Yes, you do normally need to add a pull-up resistor to the RESET line. \$\endgroup\$
    – Armandas
    Mar 18, 2016 at 11:15

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